Upgrade from TW Acustic Raven AC-3 to what?

Alectiong, Try all the tweaks first then think about getting a Koetsu Coralstone Stereo cartridge and a Koetsu Coralstone Mono cartridge, two Graham Phantom II arms or one arm with two wands and mount your TW...AC-3 on a Minus-K. This is the path I'm thinking about for my TW...AC-3. If this and your tweaks don't work you might think about the mounting your arms and cartridges on a TW Black Knight. Failing that, going another route like the Continuum Caliburn, Cobra and Castellon might be satisfing. Let us know how things go.

Stiltskin, I couldn't even recommend you following my advise.
Neither in selecting the main course nor in high end-audio.
Extremely expensive, not on the menu at all but special ordered, very special spices and only for the very educated and seasoned taste.
I stopped eating meat in the very early 80ies....

Hmm, I take it your talking about a personal culinary delight produced from a vegan?

Alectiong, I agree with your present course of trying to perfect or improve upon what you already own. Along those lines you might want to consider the heretical idea of going backward to only one motor driving the Raven AC. If you go that route, you might also consider the introduction of a passive roller to wrap the drive belt more closely to the circumference of the platter. (For example, take a look at what is done with the new Artemis Labs turntable.) One of the other forum members has made a similar device for use with his VPI turntable, and he is very pleased with the improvement. This strategy reduces belt creep, a bugaboo of belt-drive. A machinist could make the needed part for you. Alternatively, you might consider driving the platter with an outboard idler wheel, a la Teres rim drive. (Dertonearm is sure to jump/dump on that idea, and even I have my reservations about the particular way in which the Teres rim drive was designed, but reports from end users are in general favorable.) These ideas would be in addition to suggestions submitted by others, such as use of Minus K, etc. In any case, I encourage you to "think outside the box".

Using a rim drive will make all efforts for minimizing outside vibration coming towards the platter and thus towards the tracking process obsolete in one single move.

Ain't that the truth. Funny how so many end users find the net result to be simpatico. I am an agnostic, haven't heard it. But I do love my own Lenco L75 with PTP in slate plinth. I am sure you have made an uninformed negative judgement of that as well.