Plain vanilla MP3 is a very old codec. There are newer ones that are much better.
Try 320 LAME and balance the line level. Compressed files are often a little quieter than the originals, presumably to avoid clipping during compression. Also try AAC 256 VBR. AAC is as good as LAME 320 at 256. Both of these are better than 320 MP3.
Edited by bigshot - 9/14/12 at 5:01pm