Upgrade Marantz 5004 CDP to what ?

I would get a new preamp first and keep the Marantz for now. A preamp would make a bigger difference in SQ.

I still say that a preamp is most likely the best upgrade. That said:

"05-14-14: Bob_reynolds
From JA's measurement sidebar in Stereophile:

The Marantz CD5004's measured performance indicates that its intrinsic resolution is better than is needed by the CD medium. That it can offer this level of performance for just $350 is astonishing.

I'd look elsewhere than the source for the sonic tweaking you want. Speakers would be my first choice, but maybe a tube buffer would get you there.
Bob_reynolds (Threads | Answers | This Thread)

05-14-14: Darkstar1
I appreciate all the responses. I am aware of the stereophile review. It is indeed a great CDP. I'm not really trying to tweak my timbre or sound. I just want more detail, more of a layered soundstage and maybe a little smoother sound. The smoother sound is the least important as it's pretty good in this area already."

You're only focusing on half of a CD player here. The digital half. To be successful, you need to consider the analog portion as well. That has at just as much, if not more, to do with how a player sounds. A good place to start would be to look at CD players that are made by companies that make other products you like. For example, I like Ayre. The Ayre "house sound" is present in all their products (at least I think so).

Now look at this quote:

"It's hard to swallow that upgrading a $300 CDP is not the solution when my speakers and amp cost so much more."

Nothing could be further from the truth. Sometimes the cheaper component sounds better. Just because something costs more doesn't mean its not as good. Going by price, I feel, is not the best way to put together a system. Pick your components based of sound quality.

"I wish I could hear some Acram cdp players I have read very positive things about them in the forums."

"I have a creek tuner that I bought for 90 bucks on here and it's smoother and provides more depth and layered soundstage then the marantz. I would not say it has more detail though. This experience has made me think a source could change the music's presentation on my system. That is what leads me to believe I should be able to get what I am looking for with a better CDP."

This is why its so important to demo equipment. Results can be relative and will vary depending on personal preferences. I have an Arcam 33 and like it very much. Compared to my other players (both Wadia), the Arcam doesn't do the audiophile stuff (imaging, dynamic contrast, scale, detail.....) nearly as well. Its a more forgiving, easy to listen to kind of player. I use it, for the most part, on recordings that don't sound good on the Wadia.

"Looking for more detail a smooth sound which can expand soundstage particular depth."

That's you stated goal. I'm not sure an Arcam would be the best choice. But only you can make that decision. One other thing I would mention about you goal is, for the most part, the qualities you are seeking to improve upon, have more to do with the analog section of the CD player than the digital. I would focus there. (Or a new preamp!. Sorry, I know you're probably tired of hearing me say the same thing.)