Upgrade Help: CDP or DAC

Yes, I meant to include the coax output; it is the preferred connection from transport to DAC. Momentary lapse.

YES ! keep the Marantz as a transport and get a Solid state or Tube DAC! There are so many out there,I would recommend you look at something from Parasound,Musical fidelity,cambridge audio,Nuforce..I use a crappy jvc mini system to send a optical signal to a Monarch Audio DIP then out using XLR cable to a MSB Technologies Nelson DAC...the sound is simply awesome.

Matt M

Addressing the actual starting point, improved CD data reading, can reduce perceived brightness and very impressively improve listening enjoyment. Beautiful detail resolution and enhanced bass slam are just part of what you will hear. The goal is a relaxed, natural, full range sound which is "all there"
From Herbie's Audio Lab you could try the low cost Super Black hole CD mat to damp microvibations.
From Machina Dynamica a range of modestly priced enhancers is available, most notably Sonic Tonic anti-static spray to label side of CD, Code Turquoise strips to line CD tray of transport mechanism, CD Re-Animator for data surface of CD. Promethean mini-spring isolator supports beneath the CDP/ transport, and under outboard DAC if you later go in that direction.
This type of tweaking is rewarding if you don't mind the little bit of audience participation required to get better sound.

It likely that most of the perceived brightness is coming from the relatively inexpensive internal DAC built into the 5004 ($350 retail I believe). The analogue output stage likely also contributes. A newer sub $700 externalDAC can improve on this. They also differ in SQ so do your research.

Look for a tube dac