Walt,
Sounds like things are getting close. I listen to a lot of cello and find it to be a great instrument for tuning the mid bass. If cello recordings are heavy to my tastes, I figure I have a problem to solve. From my explorations, anything can contribute …room modes; synergy (or not) with your source, speakers, cables, power and tubes; but also tastes. I prefer an open and detailed sound that is not cool, and it sounds like your tastes may be in this general area??? If you tune the system toward this end, within the foundation of what you have, you will likely get more ambiance, detail and clarity, while reducing heaviness…For me, in this room, they tend to go hand in hand. Reduce low intensity/increase openness and detail.
I think you said earlier that you had no muddle or boom per say???? If this is the case, and you are close as-is to your tastes, and not too clear/bright, you can probably compensate for now with tubes and speaker placement.
Sounds like bringing the speakers together helped. Can you bring them further from your wall??? Away from corners??? Change the angle a touch??? Getting the rack out of the corner (where bass wants to stack up) sounds like a good idea. And feet? I found the sorbothane ones to contribute to low-mid bass muck. As do vibrations in general. I don't have maple blocks, but probably should. I do use Herbies Audio Labs lampblack balls in Isocups, with stainless bases under the Torii, and tenderfeet under components.
http://herbiesaudiolab.net/isocup.htm Also, I use his tube dampers. Can't say if these are the best solutions, but they smoothed out my system quite noticeably by reducing vibration/microphonics.
VRs offer great potential to incrementally tune the sound. Did you get some OB3s? If so, some OC3 or OC3Ws will further reduce low-mid/bass heaviness, and OD3 even further. As you go up the alphabet, they progressively lower the grid voltage, toning the amp down, and with that…reduce density and tighten bass.
Also the OC2 input tube regulator can be replaced with a OB2 relaxing your input tubes. Voltage Regulators are cheap and I would go further with those. With an OD3 and OB2, you would have the amp toned down considerably from stock.
Finally, 5AR4/GZ34 rectifiers tend to tone back and tighten the bass, particularly cryo'd JJ GZ34
http://www.cryoset.com/catalog/product_info.php?products_id=47&osCsid=4525ec6ebc...These have an open and tightish character, similar to the tungsol EL34.
Tube play. I really enjoy it, but not everyone does. Lon for one! But to get some beautiful sound....the above is the most efficient way I know to see if you can be satisfied before going to room stuff. None of these tubes are expensive.... in fact to get pairs of all of them together would be less than a just OK pair of interconnects.