OP: I read your post about staying the course for now - with some tube-rolling.
Just wish to toss out another possibility. The imagery in my system tightened-up noticeably when I implemented a grounding system. I use the Synergistic Research tech since the grounding methodology is integrated into my SR cabling. Other companies offer their own versions, such as: Shunyata Altaira - and Puritan Audio Groundmaster & Puritan Audio Route Master.
Another inexpensive way to experiment with grounding is this device - which I also use.
Curiously, I discovered that grounding will also reveal any noise that might be in the system. In other words, if music sounds worse with grounding, then there’s a dirty power issue lurking somewhere that needs to be addressed.