I own a Marantz CD67SE and IMHO it's a lousy transport, but a reasonable CD player.
The root of the problem is that Marantz players have very high jitter on their digital signal (both internally and externally). This is apparently what gives them that smooth sound, but it also means that if you attach an external DAC that does not have built-in reclocking the sound will be little different ... because the limiting factor is the signal jitter, and NOT the Marantz built in DAC or analogue output stage.
This is exactly what I heard when I connected a Monarchy 22A to my CD67SE ... no change.
I also own a Mission PCM 7000 ... an ancient player but a good one in its day. Adding the Monarchy 22A to the Mission made a significant improvement, presumably because of the very old DAC technology in the Mission, but with a lower inherent jitter on its digital output.
I think external DACs are very transport dependant, especially when the DACs do not reclock the signal (the Bel Canto does reclock, I believe). Adding DACs to a mid-price CD player is a bit of a crapshoot in my experience.
So, in summary I think you may end up wasting your money adding a DAC, because the DAC is not the weakest link in the Marantz changer, its the jitter in the datastrea. I think you'd be better off either having a clock upgrade on the Marantz, or just selling it and buying a better CD player. If you're desperate to get an external DAC make sure it is a reclocking DAC or budget for a jitter reduction device such as a Monarchy DIP, or Audio alchemy DTI. I have used the DIP to very good effect in my system.
