Well What if the XPA-5 IS a high end amp?
What quality is it lacking to you that precludes it from that criteria? It couldn't be power, because chances are you're probably not even nearing the max capability of that amp.
Is it an intangible quality?
Is it a matter of build quality? Are you willing to spend 5X as much on something that might last you 3X as long?
Is it a matter of perceived sound quality?
Is there an aspect of the XPA-5 you feel you can reliably hear? Are you just hoping to take your speakers to the next level? Does a next level even exist? If this is a tangible quality, how can it be quantified?
Or are you looking for a change rather than an improvement?
Are you looking to get more environmentally friendly with a more efficient design?
Do you want something built in North America?
Do you want something prestigious in the audiophile community to avoid being scoffed at by people with more money in cables than you've put into speakers?
Do you just want huge 100lb monoblocks to set on the floor?
Sorry, I don't mean to take this thread along the dreaded direction of "amp discussion".... I'm just thinking out loud here - "High end amp" can have so many meanings to different people.
To me personally a high end amp
1) Is transparent to the signal.
2) Looks elegant and pretty.
3) Is efficient with very low heat and with plenty of power to spare.
But to another person high-end amps consist of what I consider dreadful.
To me, your XPA-5 is excellent/High-end and while I might be inclined to take a spray gun to it - I'm just trying to understand your perspective / where you're coming from.