When I was upgrading from my Nakamichi PA-7AII (A Nelson Pass Threshold design) I was convinced I wanted dual mono's. I tried the PS Audio M700's and The Schiit Tyr (both dual mono), but while they did help with the soundstage width and depth, they clipped. Turns out my 30+ year old power hungry Accoustat 1+1 will occasionally draw a 0.5 Ohm which was not a problem for the Nak.
I contacted Nelson Pass and sought his guidance. He directed me to the XA-25. If there was not enough power, then the 30.8 was the next option, but he felt the sonic capabilities of the XA-25 were better and would be a great match for the Acoustats. I was concerned there would not be enough power because the Accoustats have an efficiency of 82 or 83 db depending on which source if referenced. I do help the efficiency with an active SPL Crossover allowing the dual Rythmik F12SE subs handle the bass. The XA-25 handles the speakers amazingly well. The only upgrade I would make would be if a dual mono version of the XA-25 became available. Nelson's person system has a pair of XA-25 as dual monos.
Try the XA-25. If you don't like it, then go for the 30.8.