What cd player or cd transport/dac is next for me?

I have a ML 335, ML 380S, Dunlavy SCIV's, Harmonic Tech Magic Ones biwired and Stealth Gold interconnects currently with Sony SCD-1. I had a Resolution Audio CD55 for about a year. I found that the redbook play of the Sony and CD55 were comparable with different strengths, but similar enough that I characterize them as of the same class/level.

I wish to make a significant shift in cd play. First, is it necessary in your opinion to go to the top of the heap to get dramatic improvements? Is used equipment available in your opinion that will yield those results at used prices?

I have heard the ML 39, EMC-1 ML 30.5 & 31.6 in similar systems to mine. Are the new generation of mid-level cd units dramatically improved over the prior generation? (Ml 39/ML 39S, EMC-1 upgrade)

I look forward to useful ideas for improvement. All other thoughts I suspect will be appreciated also!

Bill E.