Jenny -- You may be thinking of the ability (or inability) of USB 2.0 interfaces to handle 24/192 without intermittent breakup. Any reasonably contemporary cpu, such as a 2.5GHz (not MHz) Core 2 Duo, will not be the limiting factor in a computer for any audio format. And transferring via firewire (instead of USB 2.0) will also easily handle any audio format without breakup (firewire 400 being designed to handle the dv (Digital Video) format, which has a data rate far higher than any audio format).
USB 2.0 (the current usb standard), on the other hand, while theoretically capable of an even higher data rate than firewire 400, in practice will intermittently drop down to much lower data rates. That is because it utilizes the cpu extensively, in contrast to firewire which is supported mainly by the interface chip. And the cpu will tend to get interrupted periodically to support other processes which the computer may be running in the background.
24/196/2 channel audio corresponds to a data rate of slightly under 10 megabits per second. USB2.0 supports a theoretical maximum rate of 480 megabits per second, which in practice is invariably much less at times, as I indicated. I don't have any specific experience with Mac's, but I suspect that success or failure for real-time streaming would be dependent primarily on how clean the software installation is, and how many background processes the cpu has to support in addition to streaming the audio.
With firewire, on the other hand, I would not expect there to be any problem.
BTW, since the Sound Devices 702 I suggested can capture to an internal flash memory card (in addition to streaming real-time via firewire), and the file can be subsequently copied from the flash memory card to the computer, all of this is a non-issue with respect to that capture process.
HTH,
-- Al
