First of all, what is your budget? If the Marantz is in good shape, then maybe the choice is to buy a DAC, a good cable, and use the CDP as a transport. Decide if the Marantz has a few more years of life.
If none of your CDPs are in good shape or too old, then you could move up to a high-end spinner.
If none of your CDPs are in good shape or too old, then you could move up to a high-end spinner.