Ditch the Marantz for an Audio Van Alstine stereo amp. Look here:
http://www.avahifi.com/
Absolutely can't be beat for the money. The FET Valve 350Ex will knock your socks off for $1750. Here's the info:
http://www.avahifi.com/root/equipment/amplifier/fetvalve_350ex.htm
A high quality amp - the choice is really yours :-) - will certainly improve your system MUCH more than a transport change. I'm not saying all transports sound alike, but you've got a decent one and your amps aren't really up to snuff.
Good Luck!
Ed