Saw them live here recently (first time) and was extremely disappointed by the sound, as they were amplified, of all things! It took away from the delicacy and nuances of their instruments, but the performances compensated -- they are extremely dynamic and have the tightest rapport of any chamber group I have seen.
Kronos is an amplified quartet. That's an aesthetic decision they made several decades ago, & it was determined by the requirements of the repertoire they were taking on. They see it as actually enhancing the delicacy & nuance of the instruments, since they are doing things with dynamics & timbre which simply don't translate to the scale of the concert halls they generally perform in. I could go into the whole philosophical & acoustic underpinnings of this approach, but that would be lengthy & boring to everybody here. Suffice to say, it's not something that is thrown together casually, but the result of thousands of concerts they have performed & thousands of concerts that I've mixed, over the last nearly 40 years.
I have over half of their recordings, and that's saying a lot. Am having trouble tracking down the rest. I relate to their musical sensibilities and share them, and am grateful to them for opening the minds of classical programmers (stations, concert series, etc.) to embrace a wider definition that includes the music of other cultures (and also instruments not traditionally associated with western classical music).
Nonesuch tends to keep most of its catalog in circulation, but I find most record stores only stock the best selling half dozen Kronos releases. You might have to track them down on line. And there are some pieces available as downloads only which were never part of any CD release. Check iTunes for those.