I want to record my amp directly to my computer. I have the sound I want and I don't want to mic it. I have a H&K switchblade 100 but it has no line out. It has a midi "in" and "thru" ports. Can I record by just using a simple audio interface? And if so how would I connect it through my amp?
If this is the correct amplifier rear view it appears that there is an effects send and return jack socket. The send signal should be line level and should interface with your recording equipment fairly well.
Either the send or return socket will disconnect the pre-amp from feeding the amplifier when a jack is inserted (because it's expecting that you want to process the signal externally and therefore must break the internal connection). If you find that this happens when plugging in to the FX Send then you'll need a signal splitter. Send one split to your recording equipment and the other to your FX Return.
You can only properly record the direct output of your preamp if the guitar amp has a built in DI box, and therefor likely an XLR output socket. Even if your amp has this feature, you will find that the direct out signal that you may record does not sound the same as you hear the amp in your room. This has to do with facts as 1; the speaker of your amp greatly colors the tone, and 2; room ambience. In short; if you are really satisfied with the tone you are getting from your guitar amp, the only way to truly capture that as close as possible is using one or even multiple microphones.
If you were to really want to record from a direct signal, say because you can't crank the amp as loud as you'd like because you live in an apartment, you should look into speaker simulator boxes. A famous example of such a box is the Palmer PDI-03. In that case you would connect the preamp output section of your guitar amp to the Palmer speaker simulator, which has a dummy load built in, and from which you can then connect it's XLR output to your interface and record directly into your DAW e.g..
You mentioned that your amp has MIDI in- and outputs; MIDI can't carry an audio signal so you can't use them to record sound. MIDI is used for "PC" (Program Change) and "CC" (Control Change) messages, so say to turn on and off effects or switch from channel A to channel B for example.
Another option is to do what I do: I plug my guitar jack onto a mixer (Mackie, Berhinger) - and take the control room or tapedeck send output into the guitar amp. I have an external effects unit (nanoverb) that I loop through to get the sound I want, then the mixer output goes to the sound card.
The only way you're going to duplicate the sound of your amp is to put a microphone in front of it, the nice 'crunchy' sound from the small tube amps is a combination of the preamp tubes, the power tubes, the speaker, and the cabinet.
Some of the effects units try and duplicate the sound of different speaker cabinets, but the ones I tried didn't sound anything like a tube amp.
Most of the sound people are going for is a nice compression effect that is a result of how the power tubes drive the speaker, through a huge output transformer. The plate (output) voltage one a 6L6 tube is ~500 volts! That combined with the grid heater and screen voltage all droop when you play a loud chord or note, the result is a very pleasing dynamic compression on the speaker output.