Simple! Get an insert cable and plug it in to channel one or two in the back of the firestudio.

Its a tip ring sleeve 1/4 inch jack, and I just answered this question 2 min ago:

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Happy recordings,
Bret

Please note that on the whole, software compressors will be easier to use than hardware compressors. They might not impart a "sound" but if you get a cheap hardware one, you'd be as well using software - hardware adds noise, software uses CPU. Depends on your workflow (analog/digital mixdown) etc.

Which DAW are you using?

You can always route an output on the DAW into the compressor and then back to the input if you want an analog compressor on the track.

There may be latency introduced when you do this. You will have to offset the track to the amount of delay. Use a percussion track to find the amount to offset. This is one way to get the amount of offset on the destination tracks.

jammster nailed the same thing I would have recommended to you with your current your current equipment scenario. Your interface is not quite like a analog console or pieces of boutique equipment integrated together. So you just have to approach it a little differently.

If you have an external preamp? What are the things I might recommend would be to simply utilize in a " Y " cable on the output of the preamp. One goes directly to the recorder's input track. The other side of the Y cable goes to a hardware compressor. The hardware compressor will then feed another track on the recorder. Now you have both from which to choose from, individually or in combination.

I actually liked recording with compression. There is actually a really good reason to do this & a little goes a long way. What you actually accomplish by recording your compression is to actually increase digital resolution. If your levels are Higher by compression while recording, you are not falling into the lower resolution LSB or, least significant bits. So in an audible way a 16-bit analog compressed recording can actually appear to have the resolution similar to a 24-bit direct recording. And in the mix, this can produce a different color to the final product. I don't care if compression and/or limiting cannot be undone. I don't care because I know how much not to use. In the hands of the inexperienced, this is where the trepidation enters. And the same holds true for recording with some equalization. I make things sound right to me going in. And that's because I'm experienced enough to make those professional calls. You wouldn't become a driver at the Indianapolis 500 without some kind of prior experiences & track record. The same holds true here. Let your ears be your guide.

Errors Inc.
Ms. Remy Ann David