Great question for Pass Labs or Reno HiFi. You should try contacting them directly.
I have the XA160.5 driving the Magico Mini 2 (4ohm, 86dB). It is a very difficult load but my 160.5 seem to be more than powerful enough. My room is only 16' X 15' X 7.5'. The needle never moves indicating that it does not leave Class A. It actually did move once, slightly, during the Sheffield Drum Track LP at full volume. I have heard the the 600.5 but not in my system. They, too, are very powerful. I think it will come down to whether or not you want to remain in Class A. I don't think either option will run out of power unless your room is huge and you listen extremely loudly.
I don't know how the subs would effect things. I would expect the soundstage information to change with the subs on, but are you sure that that fact alone indicates that you don't have enough power. You should be hearing more low level room cues with the subs which would change the perception of the soundstage.
I have the XA160.5 driving the Magico Mini 2 (4ohm, 86dB). It is a very difficult load but my 160.5 seem to be more than powerful enough. My room is only 16' X 15' X 7.5'. The needle never moves indicating that it does not leave Class A. It actually did move once, slightly, during the Sheffield Drum Track LP at full volume. I have heard the the 600.5 but not in my system. They, too, are very powerful. I think it will come down to whether or not you want to remain in Class A. I don't think either option will run out of power unless your room is huge and you listen extremely loudly.
I don't know how the subs would effect things. I would expect the soundstage information to change with the subs on, but are you sure that that fact alone indicates that you don't have enough power. You should be hearing more low level room cues with the subs which would change the perception of the soundstage.