Yo Drummer! Most of us are limited by the number of tracks available, and it is an advantage not to have to use up those tracks for talkback mics. As with all mics, a talkback mic needs a preamp, and then it wants to go to the headphone output in some way. More importantly, we *don't* want track bleed/crosstalk, so the talkback winds up being recorded on some other track. These are among the main reasons that you need a separate amp for headphone distribution.
I use the predecessor of this:
http://www.8thstreet.com/product.asp?ProductCode=31910&Category=Monitoring
but there are much cheaper options, depending on how many channels you need, such as:
http://www.8thstreet.com/product.asp?ProductCode=40687&Category=Monitoring
So what do you use for a mic preamp? Whatever you have. I often use my
Zoom H4n pocket recorder, but that small mixer you have would be fine. For a talkback mic, you don't need great audio quality. So for instance, this would work fine:
http://www.8thstreet.com/product.asp?ProductCode=1084&Category=Audio_Processors
BTW- I find that talkback is the only applicatopn where I actually like a mic with an on-off switch, especially if you don't have a separate control room.
So with this setup, the headphone output of the interface goes to the headphone distribution amp. The talkback mic goes to whatever you have got for a preamp, and then to the aux input on the headphone amp. Then you can control everybody's volume level, the talkback signal goes nowhere near the recorder, preventing crosstalk, and if you are good with a mixer, you can learn to build custom headphone mixes for the deaf guy, or whatever. Good luck.-Richie