squarepusher Live Instrument Processing

Hey all. I'm in the process of developing a new performance rig and need some advice.

Here's the layout: In my band, I sing, play electric bass, and play software synthesizers in Ableton Live using a keyboard MIDI controller. Recently I've been entertaining the idea of running my electric bass into my computer for DSP purposes, running it out of my audio interface and back into my amp. Right now, I'm using an MBox 2 Pro into a 2.6 GHz Macbook Pro into Live and back out of the MBox, and although it's tolerable I'm experiencing a very slight, but noticeable bit of latency with a dry signal into the computer. My buffer size is at about 256 samples and the MBox seems to be utilizing a significant amount of the CPU while doing very little. It's obvious that I will need to find a better interface.

Basically, it's a Squarepusher style bass DSP setup. I'd email him for advice, but I understand he can be hard to reach these days.

I want to know if anyone has experience with a similar setup in which they are processing their instruments with a computer for the purpose of live performance. Do you have any recommendations as to an audio interface which has excellent low latency and wont draw a heavy amount of processing power in doing so? Any recommendations for maximum sound quality? I'm gonna install all of the gear, including a 2 channel preamp, into a rack case that I will be storing it in.

Does anyone have experience with NI's Guitar Rig, or similar programs, in a live setting? Are there any stories or bits of advice you'd like to share?

Thanks, everyone.