My past life:
http://youtu.be/fXxmmakxJNQFor info I was using an Edirol PCR-M50, an Evolution MK-461, a Roland SH-201 , a MacBook Pro (running Ableton live 7, plus a bunch of Arturia soft synths) and all synth audio (plus a few vocal and percussion effects) was routed through an Edirol FA-101 for this gig. I manage to get the latency down to about 11ms (round trip), which was just low enough for it to be unnoticeable

-Edit- I just remembered that I also use a small mixing console so I could adjust the mix a little better (also used it for some delay and reverb effects, as the venue had a very dry sound), but I forget which one i used, probably no more than 12 channels.