i'm doing this with the oz audio hm-6. you can buy it online at riks music for $260 (they also carry it at sweetwater, etc). i have outputs 2-6 running into the matrix which allow for 6 different headphone mixes. i can run protools le with my hardware buffer at 64 samples, which works quite well. this was by far the cheapest and easiest solution i could come up with.