Pradski:
With a Denon 2309 and Marantz 5001 CDP, you shouldget good music. Denon is supposed to be a musical amp, for heaven's sake.
As Moser has said have you connected the CDP properly? And are you using the PURE DIRECT mode of the 2309. In this mode, the Denon will switch off all video circuitry and give you pure 2 channel audio.
Connected properly, the 2309 may actually give better sound than any of the old models you are looking at.
Cheers