Beyond audio bitrates, I find there is a difference between listening to low quality .mp3 (even if ripped at 320 which is the new max that iTunes will do) and listening to FLAC if you have a quality setup. I'm running Focal mids and tweets with a JL amp and 12" JL sub. I can diffentitely hear the difference. I ripped all of my music to Apple Lossless (Apple's proprietary FLAC) for my iPod Classic and straight FLAC for my USB flash drive.
Alot of people debate this, but in my experience there's a difference. If you want a good converter check out dBpowerAmp. I rarely buy software, but