I have owned the Acoustats for well over 30 years. The original power amp was part of an NAD 2700 receiver ( a real beast). It drove them plus a Vandersteen 2W subwoofer). I eventually upgraded to separates which included a Nakamichi PA 7A ll which is a Nelson Pass Threshold Stasis design.
I never thought the Acoustats were difficult to drive. In retrospect the NAD had a soft clip feature that may have masked the potential clipping in ultrasonic sound at around 17000 H where the Acoustats draw 0.5 Ohms. The PA 7All never had an issue with clipping. I was spoiled. I also replaced the Vandersteen with dual Rythmik F12SE subs. Magic!
Eventually I wanted to upgrade again to dual mono power amps. My first try was with the PS Audio M700. I actually felt the sound produced by these was an improvement over the PA 7All, however there was an occasional clip which frustrated me. I didn't know what was causing it. I tried a pair of Schiit Tyr dual mono power amps. The sound was an improvement again over the M700 pair, but the clipping was more frequent.
I reached out to Pass Audio and Nelson Pass responded. He had assisted me when I was looking at the PA 7All. I was enquiring about the about the XA60.8. He said that they could easily handle the Acoustats, but he preferred the sound of the XA 25 with electrostatic, and other hard to drive, speakers. He suggested the efficiency of the Acoustats was well above the 82-84 db when the signal was being actively crossed over (I use the SPL Crossover) and probably more like 87 or 88 db. He recommended I try the XA 25. If it didn't go loud enough, then the XA60.8 would definitely be enough. His personal power amp is the XA 25 (albeit a pair customized as dual power amps). He offer to help me do the same, unfortunately my electrical skill level is deficient.
I purchased the XA25 used. I doubt if I will ever need another power amp. I typically listen at 80 db measured from 3 meters away. Peak volume for me is usually 90 db, although for larger entertaining events I have cranked it to 100 db with no issues. My old pre-amp (a Benchmark which was quite good) could not push the volume over 100 db (at 3 meters). I have pushed it to 110 db (ear splitting level if maintained for extended periods) with the LTA MicroZOTL Level 3 with no distortion that I could tell. It could go louder, but I don't know how much.
The XA 25 is an amazing amp.
On a side note, I eventually figured out the Class D power amp do not play well with speakers that have a low Ohm draw. Stay away from Class D with electrostatics. I have two other speaker systems (lower level), and Class D amps work great with those speakers (KEF and 3D Acoustic -a Rogers speaker clone from the late 1970's.
If you can borrow an XA25, I would suggest trying it with your Acoustats. I have not heard the 2+2, but I have read that they are little more efficient than the 1+1. I am not certain if they have a similar low Ohm draw.
Best of Luck,
Ralph