MCN,
I haven't done a comparison of the 588 vs 598. However, I can say that the 598 is very very good with std CD's. A bonus is that you can do DVD-A also, although it sounds like that is not important for you at the mo.
It would be worth getting a dealer to set up the comparison for you. In the meantime, the new range should have emerged and you will see if there's anything else to look at.

Rgds

Nick

Rgds,
Nick