Hi , I just joined the forums today and couldn't help noticing your post .
I have the US 122 ever since it showed up on my local music store's shelves , and use it with my 15" PowerBook G4 . Your post seems a bit disoriented regarding the order of the actions you took using the US 122 with the Mac .
Tascam specifically asks (written with red) at the beginning of the Mac OS X driver installation process that you DO NOT CONNECT the US 122 while installing the driver . Did you do that ? If you had your US 122 connected during driver installation , it's possible you damaged it .
What versioin of Mac OS X are you using . There are different drivers recommended for Panther or Tiger .
But after all this time you posted this I suppose you allready solved your problem , or got yourself another sound card .
Hope it's nt to late .
I've never had any prblems with mine . It worked flawlessly with every audio/MIDI application on Mac .
No pops , no clicks , good quality recording , no latency at all .