FWIW, try to articulate exactly what you are trying to change or improve. It may well be your CDP, or not.
There is probably no CDP, redbook or SACD, that matches well with all systems playing all tytpes of music. I have multiple CDP's - they each excel in certain aspects of reproduction but not all. Some sound better with one amp, not so much on another amp. Synergy is a big issue (for me anyway).
For example, I have the Marantz you asked about. I find it has an excellent mid-range and highs, but I find compared to my other units it's upper bass is a bit full. On rich orchestral music it is a bit too much. With that music my Wadia excels. I also find that in my system the sound stage is a bit closed down on orchestral music, but for small groups (classical or jazz) and solo instruments it is excellent. My system is voiced on the warm side of neutral and I'm sure that it is more the system than the Marantz that limits the system performance., but it certainly contributes.
Based on that experience with the Marantz in my present system I would not get another, but if I were running a solid state system instead of tubes I expect it would be excellent as most solid state stuff doesn't have upper bass emphasis (nor do your speakers I think). The Marantz is built like a tank and has operated perfectly for over two years now.
Be nice if you could audition one.....