Dear Alec,
Is there a reason why you have tried the matless approach yourself?
Rather than using the Millenium mat or fancy alternatives like the Zanden, why not try the Gold Spot Ringmat with the latex underlay. It's a (relatively) cheap investment which may transform your listening.
(I recall you saying back on Day 1 that you wanted to relieve the "dark sounding" tendency and enhance the soundstage? Well, the above hybrid combination delivers exactly that. In doing this, you should realise, you may have morphed from a "damped" listening enthusiast to the "undamped" philosophy... ;^)
A platform of the quality of that which you are using would enable an even bigger difference to be heard. ;^)
Final recommendations are to avoid sharing the T/T shelf with anything else and position the phono stage on a shelf under the T/T using a short phono cable (say 0.5m dual midi-coax with Earth). If you can get the motor controller onto the bottom i.e. 3rd, shelf so much the better. Also pay attention to the dressing of the phono cable as any incidental contact will affect tonearm and cart behaviour as it does act as an energy conduit. If it does contact anything, introducing a small amount of interference (don't laugh - a toothpick) as it passes over the back edge will be enough to prevent it coupling directly to the resonance of the shelf itself. I've found this to be easily identifiable in blind tests and indeed this item alone can decrease the tendency of the turntable to be "dark" or "leaden" sounding.
Doing the same "decoupling" trick with the motor cable/s is less important but you may wish to try it anyway?
Decoupling the phono stage itself may not be necessary as they often sound better without any fancy mechanical supports. Much of this depends on whether the shelves are multi-stage spiked tripods (or alternatively suspended supports). Personally, I didn't see the point in trying to turn an unsuspended table into a suspended one but many seem to recommend this so I suppose that must also be considered an option(?)
Apologies that I haven't worked my way through this thread yet and am unaware if anyone else has made similar recommendations which are very simple and virtually free(!) or indeed if you've already done most of what I've suggested above?
Anyway, you can afford to cherry pick any advice you feel is easily actionable.
All the best,
