Motu 828 Tips, why is mine sucking? Options

[mook noodler]

Okay, so here's the scoop: Just got DP4 and an 828. I'm running them on a dual 1.25 g4 Power Mac (FW800, OS X only), 10.2.5, 768MB RAM, 120GB LaCie FW drive. When I'm just doing midi sequencing (midiman 4x4) everything is perfect. It starts to suck when I try to record audio while the midi tracks are playing. I can't record more than 1 minute of audio before it stutters DURING the recording, even if it's just one track. The CPU monitor and the Performance monitor say everything is fine; I'm not anywhere close to overloading the Mac. Am I missing something? I've tried all kinds of different buffer settings.

something else that bothers me about it: If I'm playing back midi tracks through inputs 3-4, I can't listen to myself play guitar on inputs 1-2, even if I select "audio thru". What is the point of 8 inputs if I can only listen to a pair at a time???

Maybe I just have a bad unit. Has anyone else experienced this? Thanks in advance!