One thing you need to be certain about before you go much farther is:

What is the exact nature of the quality problem you're having, and which "stage" is causing the problem?

For instance, it could be something really simple, like bad rips from AudioCatalyst or your CD drive. If the original WAV file isn't landing on your hard disk intact, no amount of bitrate increase is going to help it. There's some non-obvious errors that can creep into a rip, such as a screwed up stereo image. See the FAQ entry on this subject.

Next, there are the obvious choices about encoder and bit rate. In my experience, even the Xing (Audiocatalyst) encoder can produce great MP3s. Then again, my ears aren't golden. If you're really hearing troubles with the Xing encoder itself, then you've got really good ears, because the differences between Xing and LAME at high bit rates are very subtle.

Finally, if you're comparing a CD to something played through the Empeg, you need to understand that the Empeg is equalized differently from the CD. Perhaps your complaints about quality are simply because the Empeg is playing "flat" and the CD has certain frequencies pre-boosted for you. Most consumer CD players boost the bass a bit to increase warmth (even if your bass and loudness are set flat on the CD player's control panel). Try playing with the Empeg's loudness and EQ a little.

___________
Tony Fabris