What should I upgrade first amp or preamp?

on the other hand, the move from the XP10 to the superb XP20 is both a significant step up and much less costly than moving up the amp line...

While the XA30.5 probably has all the power you need, my Pass dealer had told me that in the XA series, more so than the X series, the overall sound quality improves more each step up the line.

I would speculate that a major reason for that would be that the higher powered XA amps continue to operate class A up to considerably higher power levels than the XA30.5. But considering the OP's listening levels and speaker sensitivity, it seems likely that his XA30.5 goes into AB mode rarely if ever.

Regards,
-- Al

Not to mention that even though he mentions the XA100.5, he would have to double the amount he states he wants to spend.

What about dynamic peaks Al? I've read your threads on that and wonder if that matters less at low volume?

JL, as the average volume level is reduced, the volume of dynamic peaks will be reduced by the same number of db. Per the calculation methodology I described in the thread you are probably referring to, with the OP's speakers listened to at a 3 meter distance the XA30.5 wouldn't leave class A until levels of around 97 db were exceeded. (It's coincidental that the 97 db figure in this case is the same as in the situation in the other thread).

I doubt that 97 db would be exceeded on dynamic peaks more than rarely (if ever) in the circumstances the OP describes.

Best regards,
-- Al