Best upgrade path?

wait for the itch to pass, or get into vinyl...where you'll have a world of issues other than upgrading your great components.

Your system sounds wonderful! If you’re not sure what you seek, save yourself some money and be happy with it. If you have the itch, and need to upgrade then consider these ideas:
(1) If you live in your own home are you using two dedicated circuits (amp/CDP) with high end AC outlets such as the Porter Ports for example? That would make a significant difference in detail, transparence, and perhaps more bass slam.
(2) You never said what type of interconnects and speaker cables you use. An upgrade might be desirable.
(3) Plinius makes several amps that have the ability to play class A/B or with the flick of a switch solid class A. Believe it or not the class A is an improvement. That said, I should know. I own a Plinius 8200, SA-50, SA-100 and SB-300.
(4) Have you done any sonic room treatments?

Best regards,

"...get into vinyl...where you'll have a world of issues other than upgrading your great components."

Chuckle, chuckle. Good one. Profound words, indeed.