jon- Rob Gillum at CoherentSource Service makes the PXO modification to match the Thiel speaker of your choice.
audiojan- your experience is classic: distance from the walls makes for better image and evenness, but those very walls were reinforcing the bass. In your situation a subwoofer makes sense . . . unless you can move the speakers out of the alcove into a more normal, rectangular space.
unsound - indeed. They are pigs to drive well. This year I have read and studied widely, and the over-arching problem of Thiel speakers is driving them. The amps referenced on this forum work and many of those are the amps Jim used in development. Krell fpb, Levinson monoblocs, big Bryston, big CJ, Classe DR. The common thread in those designs is their ability to deliver large current streams at high voltage without distress. Others here have recommended other amps, which are no doubt suitable, but I have not heard them. However, when an amp can't deliver the required current, the litany of complaints arises.