I regularly do 4 channels of 24/44.1 with an emagic A62. I haven't tried 6 channels but it's supposed to work fine (USB 1.0 btw). With the right software, CPU usage is very low. Disc activity will also be low as this still isn't much data to write. I run it with win2k, ASIO drivers, and Kristal to record (freeware).
Can be had for $200 used, $275 new. USB bus powered but external is possible. Don't know what the power draw is but it doesn't seem to cut my laptop life much. Unscientifcally I'd say I went from 4 hours of power (w/self powered UA-5) to 3.5 hours with the A62.
The main catch with multichannel audio interfaces is that you need to control gain properly in front of the device. i.e. it takes line level signals and doesn't have any knobs to turn for more or less gain. So if I'm recording the board and don't have a cooperative soundperson who's willing to turn the matrix output up or down, then I run the UA-5 in the chain just so I can control the levels.
Feel free to ask questions - not many people seem to have these as most tapers just do two track. I got it after doing one too many sbd/mic mixes with sources clocked differently. Makes life much easier when you don't have to deal with time drift.