Thanks again for all your responses. Here is my reaction to your comments so far:
Some say start at the front end, either a better CDP or an outboard DAC, followed by pre-amp. Audiofeil says no, upgrade the speakers. Say I can get $2500 for my Adagio's and kick in another $2k. Audiofeil, what would you recommend used for ~$4.5K that you think would best the Adagios ?
Others suggest room treatments (no doubt a good suggestion), AC power conditioning, power cords, and isolating the CDP from the AC to the other components. What specific recommendations would anyone recommend for AC conditioning, power cords, and isolating the CDP ??
Dave b suggests adding AV123 supertweeters. I am really intrigued by this suggestion. The Adagios have circular ribbon tweeters that are supposedly flat to 30KHz, and I am 56 yrs old. I think my hearing is pretty good, but I'd be surprized if I can hear beyond 16K. I'd like to hear more from you as to why you think adding a tweeter that extends thehf response from 30K to 50K would add to my listening experience ? The reason I ask is that this upgrade is relatively inexpensive, so it is certainly worth considering.