There is software that will analyze an audio file and calculate how to re-synthesize it, but it is geared mostly towards additive synthesis and frequency modulation synthesis.
In the case of additive synthesis this is logical, because if you know the level of each harmonic of a sound, you can recreate it exactly with additive synthesis. The drawback is of course that this recreates just a single-cycle wave with perfect-multiple harmonics, while it is often the slight inharmonicity and the changes in timbre, pitch and amplitude over time that make a sound recognizable and interesting.
In the case of FM synthesis, software to re-synthesize existing sounds emerged primarily because FM synthesis is far from intuitive, and most people found it near impossible to dial in the sounds they wanted to make on e.g. a Yamaha DX-7.
To an extent, you can use a plot of the harmonic spectrum of a sound to help you recreate it using subtractive synthesis. If you have a basic knowledge of the spectrum of the waveforms typically found on analog synths (sawtooth = all harmonics at level 1/n, square wave: only odd harmonics, pulse wave with 1/x duty cycle: all harmonics with a dip around every x-th harmonic, triangle wave: only odd harmonics but at level 1/n^2, sine wave: only first harmonic) you can look at which harmonics in the sound are the loudest, and see if they follow a pattern that you can re-create by combining, detuning and filtering the basic waveforms.
Tutorials about how to re-create certain sounds will tell you e.g. that an electric bass is best synthesized with a narrow pulse wave and low filter resonance, or that strings require multiple detuned sawtooth waves or pulse width modulation, combined with a chorus effect, etc. However, this knowledge doesn't really help you if you want to recreate the sound of a different instrument, or that strange bird-like siren you once heard in a movie. At that point, I think experience of fiddling around with a subtractive synth and trying out every setting will be much more important than any knowledge you can gather from a book or online tutorial.
If you want to explore the possibilities of subtractive synthesis to recreate certain sounds, in order to get a good idea of what kind of guitar synth setup you want to buy, my advice would be to buy any subtractive synth that has a good feature set and a knob for every feature on the front panel, and just experiment with it for a while. It needn't be expensive, vintage, real analog, stylish or from a big-name company, any synth with decent quality should be enough for learning and exploring.
I had a look look at the synths in stores now, with the following wish list of features in the back of my head:
Two detunable oscillators with the standard waveforms including pulse width modulation and white noise, oscillator sync, ring/amplitude modulation, and frequency/cross modulation.
A 24dB/oct (4-pole) resonant low-pass filter, capable of self-oscillation, with switchable key sync, plus a high-pass filter. Possibly also a 12dB/oct filter option.
Two four-stage ADSR envelopes with switchable key follow.
A low frequency oscillator with delay/fade-in and different waveform (preferably both sine and triangle).
An interface where every feature has its own knob or button on the front panel. I think this is crucial for an enjoyable synth experience, especially for your use case.
Key Velocity is a bit of a dilemma. Many classic synths didn't have it, but on the other hand it can make a sound much more alive, even if it just modulates the amplitude. With a background as a guitar player, you'll probably find a synth without velocity to give a somewhat sterile playing experience.
Chorus effect isn't strictly necessary, and was usually added to fatten up the sound of a single-oscillator synth, but it is useful on other synths as well and some classic synth sounds rely on it, especially strings and organ sounds. But as a guitar player you may already have a chorus effect that you can run the synth output through.
In the affordable part of the market, there are a few smaller synths with most of the features listed above, although they each have their drawbacks. The Roland Aira System-1 is a 4-voice digital synth, and it is the most fully-featured in this price range. Its main drawback is the 2-octave non-velocity keyboard with limited key movement; you'd have to try this out for yourself. (There is a rack version you could use with a keyboard of your choice, and there is a larger version, the System-8, with a better keyboard and effects, but the same garish looks).
Similar is the Korg Minilogue, which is a real analog 4-voice synth, but it lacks some features; e.g. the wave shape of the two oscillators cannot be modulated independently. It also has smaller than standard keys (again, try it out).
If you don't mind the ridiculously small form factor, then the Roland Boutique Series JP-08, a digital recreation of the legendary Jupiter-8, could also be interesting, but you'll only find these second-hand. If you combine this with a decent controller keyboard instead of the boutique series own K-25m, this would make a great introduction and learning setup.
If you don't mind the synth being monophonic, then the re-released ARP Odyssey is an analog classic, with many interesting features, and in my opinion more interesting feature-wise than a SCI Pro-One or Minimoog clone. Have I mentioned that it's a classic?
If you're interested in going semi-modular, there is the Behringer Neutron. It is analog and has an extensive modulation patch bay which allows weird and unusual things that most hard-wired synths can't do. Drawback are that it's monophonic and doesn't have its own keyboard.
(There are also the Behringer DeepMind, Roland SH-01 Gaia, and the Arturia range, but they each have drawbacks that make them less suited for learning subtractive synthesis. At the higher end of the price range are various interesting options from Dave Smith, Sequential Circuits, Novation, Nord and Access.)
If you're not just trying to decide which guitar synth to buy, and you want to dive into the synth world and invest some time and money in it, experimenting with a graphical modular synth programming environment like Reaktor (or a second-hand copy of an old version thereof) will probably teach you the most about sound synthesis. It allows you to build exactly the synthesizer or sampler or effect or ... that you want to experiment with from scratch (or modify one that someone else has made), and includes oscilloscopes and other kinds of visualization, so that you can look at the waveforms while you listen to them.
Everything you read in books or online about sound synthesis can immediately be put into practice. Whether you need a synth with ten oscillators per voice, or a combination of frequency modulation and oscillator sync, or granular synthesis, or VoSim technology, or additive synthesis, or any weird scientific stuff you read about, you can try it out without needing to own a bunch of different synths that each only do one thing.
One prerequisite however, is a slightly nerdy disposition. If you have zero interest in acoustics or maths or physics or programming, you may find that there's too much fiddling around on the computer and not enough actual playing going on.
For an example, have a look at this answer I wrote to a question here about using Reaktor. The asker wanted to experiment with Shepard tones, and I didn't really understand what he wanted to do, but while thinking about it, I started to wonder whether you could build a filter bank with constantly rising or falling filter frequencies that could make any input sound like a Shepard tone, and I built such a thing with Reaktor, and the result turned out to be quite interesting and useful.
Here's another answer with a simple Reaktor instrument that also shows what the graphic programming environment looks like; you just select a bunch of parts and patch them together with wires, there's no programming as in typing in code (although you can do that if you want to in recent versions).
There are other modular environments out there, like Max for Ableton Live, but I haven't used it, and I think Reaktor will have a less steep learning curve and be a better choice for specifically learning about subtractive synthesis.
A good alternative for software would be something like the Nord Modular (look for a second-hand version G1). It's a little more limited, and won't give you all the visualization and weird interface options, but it's a real instrument that you can unhook from the computer and play anywhere, which is fun too. (If you buy a Modular G1, let me know and I'll send you some patches I made for it, which each explore a particular aspect of subtractive synthesis.)
