Beginner interface questions

Hi, Mike, and welcome to the forum.

Opinions about interfaces will surely fly here, but keep in mind that most of us, myself included, have only personally used a couple different units. So if I say that Lynx and RME are good brands, I'm only repeating what I've heard elsewhere and not basing it on actual hands-on experience or objective testing.

Hardware-wise, the differences between interfaces are not huge. Anything in the $400-$1200 price range will do a suitable job of converting your audio into numbers. Pick your interface based on features rather than mojo. That means if you need 16 simultaneous and separate inputs, you'll have to necessarily narrow the candidates to those with 16 channels. It means if you require ADAT, S/PDIF  or MIDI connections look for units with those features.

Yes, you can use a digital mixer as your audio interface. Bear in mind that some of them only offer a single output, so you're limited to recording a full stereo mix, as opposed to multiple channels recording on separate tracks. One advantage of using a mixer is that you can combine sources when it's not necessary to record each channel individually. You can also expand a mixer more easily than a rack interface.

Yes, you can have multiple headphone mixes, but only if your chosen interface has multiple analog outputs. Most of the mid-priced interfaces have at least 4 outputs, but 2 of those are your main monitor outs, leaving only 2 mono outs for headphone mixes. That may or may not be enough, depending on how you work. For me, as a one-man-band, 4 outputs are adequate (my interface has 10 outputs but I've never used more than 4).

Also consider the number microphone versus line inputs, and make sure they match your needs. Pay attention to whether the jacks are on the front or rear of the unit. Some units have 8 or more mic inputs, some have only 2 mic inputs but multiple line inputs, and some have only line inputs. Some have the mic inputs on the front panel, which can be handy for quick connections, but having them all on the front means a mess of cables hanging down the front of your rack, getting in the way of other units.

In my case, my interface has 2 front-mounted combination mic/line inputs and 8 line inputs on the back panel. I wish it had mic inputs on the backside to reduce cable clutter. If you'll be recording acoustic drums, you'll want many mic inputs as opposed to many line inputs, to save the expense of outboard preamps. Someone doing 100% in-the-box synthesizer compositions would be wasting their money on either one and would be better off with a PCIe interface.