Hey guys, I like your thinking here, and I think that mixer would work, but I thought I'd share my set up just incase it might be something you want to consider. I'm running a Firepod, so practically the same thing as the 8pre interms of ins, but I have 8 outs, and I use 6 of them. I have a Samson C-Control, which works pretty well but, like all samson products, can be hit or miss. Luckily, mine was hit, because it works great. The C-Control has 4 stereo inputs and outputs, as well as a built-in talkback mic. So I run the channels 1-2 into the mains on my C-Control, which then run out to my monitors (Speaker A) and my sub (Speaker C, I don't use Speaker B). I then also run the Cue out on the C-Control to my Behringer Powerplay rackmount 4-channel pre-amp. This gives me 4 headphone channels of the mains, and I can talkback to the Behringer using "Talk to Cue" on the C-Control. I then also run 3-4, and 5-6 into 2-Track A and 2-Track B. These are for two separate headphone mixes that go to two separate Rolls 4-channel headphone amps across the room. Then for 2-Track C, I originally had a 3rd headphone mix, but realized I don't need that many and instead leave it open for an iPod or something if the musician wants to play me something. The C-Control also has a "Talk to 2Track" button on the talkback mic if I want to communicate to the headphone mixes (usually for the drummer).
The C-Control works really great, especially since I don't have a control room, so when I need to turn my monitors off to record something live, I can just press "Speaker A" and "Speaker C" on the front of the unit to turn them off, rather than having to reach around back of my monitors and turn them down and up. And having the talkback is pretty nice too, although I mostly record singer-songwriters, and they generally track right next to me, so I don't really have to use it too often. Anyways, check it out, it might be what you're looking for, and it's pretty cheap too. Presonus and Mackie have products that are supposed to do similar things, and are of better quality, but I actually found that the Samson fits my needs better for the set up I was trying to do.