Okay, so I'm looking for advice on what's the most appropriate equipment decision for my situation.
I started with a 2007 MacBook Pro, and I eventually realized that the integrated Intel sound card really sounded like garbage. I was hearing tons of strange artifacts and subtle distortion. I tried out a Behringer U-Control UCA200 I had lying around (that's the drop-in 2in/2out USB-RCA interface they bundle with all their mixers) just to output audio to headphones, and discovered a huge improvement.
Then, I expanded my setup to a mini studio of sorts, adding a Mackie 402-VLZ3 mixer with the tape input/output connected to the UCA200. Thus, I'm treating the mixer as a control for all the audio I/O of the computer. I've since upgraded to a 2010 iMac, but yesterday the UCA200 seems to have kicked the bucket. It works for about a minute before failing completely and needs to be replugged. Definitely not workable.
So the question is this: Is there a higher-quality replacement I could get to replace the failed UCA200? Or, perhaps an entirely different kind of interface is in order. I really like the mic preamps and headphone amp of the Mackie mixer and would like to keep using it, but I don't think duplicating all of that functionality in a piece of USB or FireWire hardware is practical. Perhaps I should just use minijack-RCA cables from the in/out jacks on the iMac and forego a USB interface entirely? Seems a little tacky for some reason, but perhaps the quality on those integrated interfaces have improved from 2007 MBPs to 2010 iMacs.