Hi Steve
Just some further clarification.
Your original question was about replacing your 598. When I referred to the 800 in my previous post, I was picking up on Jeremy's comment and really referring to the 8xx series as a whole, not just the actual 800 DVD/CD player
If you have a look in Duncan's Meridian Info, it lists all the versions available (800v1-4, 808v1-6 and 808i and what their respective specs are etc).
I guess if you can go to the 808v6, this will give the best CD performance.
Hope this helps.
Cheers
Jon