I have a Kenwood Excelon Z919 CD/MP3 headunit and I love it
I use regualr CDR's but the thing is, you have to burn your MP3's have to be 192 kbs or better. The MP3's I play are music from CD's that I converted to MP3 and did it at 256kps. The sound is awesome. It's the quality of the MP3 files you gotta watch.