I think Pubul57 is right. I suspect that the X600.5 and the XA160.5 are unlikely to sound the same, even at lower volumes. My understanding is that the circuitry designs of the two amps have significant differences, and that those differences are audible, even when both amps are operating in Class A. Certainly I can say that my X250.5 and XA30.5 didn't sound exactly the same, even when both amps were operating in Class A.
Your room is quite large, and you mentioned a tendency to listen at loud levels. So it is not a clear cut decision, IMO. It would ideal if you could audition the XA160.5's in your system, to see if they have enough power for your loud listening sessions. If it were me, and I could not audition the amps, I would take a chance on the XA160.5's. I have heard the XA100.5's, and to me, they sounded absolutely glorious. FWIW.
Hopefully other Pass owners with more experience than I have will offer their advice.
Bryon
Your room is quite large, and you mentioned a tendency to listen at loud levels. So it is not a clear cut decision, IMO. It would ideal if you could audition the XA160.5's in your system, to see if they have enough power for your loud listening sessions. If it were me, and I could not audition the amps, I would take a chance on the XA160.5's. I have heard the XA100.5's, and to me, they sounded absolutely glorious. FWIW.
Hopefully other Pass owners with more experience than I have will offer their advice.
Bryon