Hi Thieliste,
I hope all is well with you- I was just wondering what you decided to do and if you are happy with match for Thiel 3.7's.
As you might recall I also have Thiel 3.7's which I simply love and use daily. I am also looking for an upgrade to my current system and I have found this thread extremely interesting and helpful. My current set up is Pass XA 60.5's, Primaluna Dialogue premium (speaking of solid state . amplification combined with tube pre), moon audio 280d dac- cabling is Nortdost Heimdall 2 throughout.
System sounds great but I do think the Prima Luna may be the "bottleneck"....it is great but i suspect that the alps volume control holds it back a bit compared to higher end preamps.
I really like the Pass labs with the Thiels but I am not necessarily married to them if I had to change them in favor of better overall pre/amp combination. If I were to put my finger on what the system is missing it is a bit of depth to the soundstage and some smoothed over detail thus not managing to extract some of the finer spacial cues. As for the rest, the rig really produces an outstanding lateral soundstage with excellent solid imaging- the Thiel's completely disappear.
I also wrestled with the idea of a high end integrated or just going with a preamp upgrade. (Well, I am still wrestling with all of this.). In terms of the latter I have to always consider the right match for the Pass amps as their measured input impedance is 17k (20k stated single ended).
Suggestions have been to try a Pass preamp exploit system synergies but others have had better experiences with other alternatives (simaudio 740p with pass amps). If I were to stick to tubes others seem to think that a PS Audio BHK or an Aesthetix Calypso (Eclipse) might be great combo's.
SO i am kind of the same boat as you and wondering what to do- and therefore I am very interested in hearing what you ultimately decided to do.