MetalGarret
Inspired
There is no sound difference between USB and FireWire. Zero.
I also think its your mackie. I'd go axe USB out. (Forgive me if you tried that already, I may have missed where you said as much)
What is your definition and damping set at?
Have you tweaked the cabs stock response much?
Firewire has less latency issues. At least for me it does.
I'm still stuck at work. USB out is the only connection I haven't tried I think so we shall se what happens.
Thing is,.the onboard Eq is turned off. Would the mixer still have an effect on it?