The iTunes converter offers both MP3 and AAC at bit-rates up to 320kbps stereo, with optional VBR (variable bit-rate) where 320 is a minimum guaranteed bit-rate.
Given that the "Hi-Fi Transparency" standard is 128kbps per channel (thus 256kbps for stereo), I doubt anyone's ears can discern the difference between 320kbps and either lossless PCM or the original analog.
Ya mine especially. Too much rock music back in the day. I convert to 128 for space.
I am concerned though about the algorithm for converting one format to the next. Is a direct bit/byte copy or decompression then compression to mp3? Like the old goofy burn to dusk solution.