Trying to test different recording techniques for my band, and was wondering about patching a guitar amp directly into my Behringer audio interface. The guitar amp had a "Preamp output", is that something I could use to patch into my audio interface? If that could work, would I have to set the interface channel to instrument level? Thanks.
Yes, you can record straight from the preamp out, but it will sound very bright and a bit annoying. That's because the power amp and speaker on the amplifier change the sound to make it more mellow and add some character. You can use EQ on the preamp out signal to make it sound more like an amp, and/or you can use a speaker simulator to make it sound more natural.
No, do not set the input to instrument level. The output of the preamp out is line level, not instrument level. Instrument level is what is coming right out of your guitar. The preamp increases the level from instrument level up to line level.