hey yall.
i replied privately, but for the purpose of anyone else needing the info...
you can do 24/48 in 2-channel via USB just fine. the MBox will only do 2 channels at once, so you'll need to do any mixing outboard, if using more than 2-channel sources. it'll take 24-bit s/pdif i believe.
the preamps sound good; they're not neve, they're not grace, but they're certainly better than most outboard pres in their price range. i'm convinced that the focusrite name contributes to the price of the mbox itself quite heavily.
it's a great box, very stable, but it's also a power hog, at least mine was, drained my powerbook quicky.
anything else, feel free to pm