I also should have clarified - I believe most DAWs are set up to only accept input from one interface at a time, is that correct? That is, you can't plug in 2 interfaces or an interface and a USB mic and record both at once, is that correct? That's a different thing entirely than how many channels of input it accepts from a given interface (as I understand it). Your example of lots of drum mics, I assume, would all go through a single interface as separate channels, is that correct?
I'm not sure I'm using the terminology right, but Audacity seems to be limited to a single interface at a time, and a limit of two channels of input (stereo) from that interface. It may be capable of more channels, I'm not sure, I haven't found any setting for that, but then again, my interface can only do two channels anyway.
No worries at all, just trying to help keep things straight.
It can be generally assumed that most DAWs will expect to work with a single interface for AD/DA, where the term "interface" is just another way of saying "a single place to deal with I/O". This can be a single piece of hardware (e.g. a Focusrite Scarlett and all its associated I/O), multiple pieces of hardware chained into a single interface (e.g. connected via ADAT lightpipe, MADI, or other), multiple pieces of hardware aggregated under a single virtual device (e.g. the aforementioned Scarlett and a USB microphone), or something like a Dante network with many devices providing I/O and connecting into a physical or virtual sound card(s). Regardless of the hardware configuration, your DAW will recognize the interface, which will make available all of the I/O it has available.
To expand on the drum mic example, you could use a single interface with 8 channels to capture 2x overheads, 3x toms, 1x snare, 1x kick, and 1x room. Alternatively, you could connect two 4 channel interfaces via ADAT (with one over USB to the computer) and accomplish the same. They will present differently in the DAW (the second interface over ADAT would be something like "Digital IN 1" though "Digital IN 4", but it will all be through a single interface.
One more thing to note is that in the previous example, all of the inputs were MONO. Unless otherwise noted, most everything in the recording world is mono at capture. Microphones, bass, guitar... all single input sources without any spatial / panning information (e.g. they're dead center). Capturing in stereo requires two microphones, or some bit of gear (like a panning delay or reverb) that takes a mono source and provides spatial information. It also follows that you would need two channels of input on your interface to capture in stereo, and would need to capture to a stereo track in your DAW (or two separate mono tracks that are panned accordingly).
Conversely, you can treat a "stereo" input/output on your interface as a pair of mono channels - this is why you might also see something like "3/4" on a headphone out.
