Mapman, I think you're onto something. The upscaling DACs seem to be doing something more, so that old CDs, from 16/44.1 masters of old sound better than their analog counterparts of the same masters. I've got some old Telarc LPs from the late 1970s. I can hardly stand listening to them on my TT, but the CD versions sound very, very good on my Playback Designs MPS-5. As you know, the MPS-5 has a proprietery upscaling DAC that takes the CD up to DSD levels, but there has to be some alogarythm filling in the blanks, adding life and exorcising the digital glaze.
It's funny, it took LPs of early digital to capture forever the horror of that. I can't believe that I actually thought those LPs sounded good back then!!! I can't stand them today, but the CDs of the same master are just hunky dory on my MPS-5.
Do "better" CDs sound superior to their ordinary CD versions when compared on the MPS-5? The answer is "yes, but not a whole lot." Comparing the CD-layer to the two-channel SACD-layer on a hybrid SACD, the SACD layer is superior, but if the gap was 50 vs. 100 on my old Pioneer, it's now down to 90 vs. 100. Now, with the MPS-5, my purchase decision is now mostly down to cost, where before the MPS-5 I might pay twice as much for vinyl or 1/3d more for SACD I'm now largely indifferent. When the SACD is available, then I'll usually spring for it if it's only 1/3d higher or so.
If you can know beforehand, it really comes down to the mastering engineers' choices. Generally reissues of non-audiophile release will sound better than the orignal CD, due to different balance levels, compression, etc. which you now easily hear. This comes into my decision process, in addition to fomat vs. price.
Dave