I've heard the CD6 before and I didn't think it was overly lean with bass.
I'd hazard a guess that the Proacs are the main cause of the lean bass. From recent experience of older proacs they sound very similar to some custom made speakers I've just got, tight and lean, great on vocals but no weighty punch on lower frequencies
What other component sources do you have e.g turntable, tuner? Do these sound lean too?
To play safe, I'd test some other sources with the proacs to make sure you really want to change the CDP first.
I'm finding that my Rogers LS55's are very hard to beat they have fantastic bass weight and it's well controlled. I'm going to test some Spendor S6e's to see if there's any improvement.
I've got a Marantz CD17Mk2 KI and the main difference is detail. I tested the Arcam 192 too and again, like the CD17 it was more detailed than the CD6000 OSE predecessor. There wasn't much difference in bass weight, just more detail all round.