I have never heard a pass product in my own system but I do have the lux550 mark II. I have tried it with three solid but different speakers. IMO the lux balances best with high efficiency vintage klipsch, which take advantage of the dynamic capabilities of the Luxman and are rolled off on top. My experience is that the Luxman is absolutely fantastic, incredible resolution and dynamics, but tends to accentuate brightness in your speakers if present.
If you can’t hear them side by side, check out Steve guttenberg review of the Luxman 95th anniversary something or other where he compares it to pass separates. He describes the pass as being warmer, rounder, and less exciting but still pretty, basically.
Perhaps you should just buy a Pass integrated (int25 would be my suggestion considering your efficient speakers) and sell the one you don’t like. Alternatively try the Luxman tube integrated or separates they are supposedly fantastic
But my real suggestion is, you will realize a much much bigger difference by changing your speakers and sticking with the amp that suits your lifestyle, rather than messing about with sources and electronics. If you want meat on bones and high efficiency, check out the Devore orangutan line. You can get used o/93s for less than any of these fancy amps you are talking about here… and in addition if you swap speakers after swapping amps, you may find the new speakers call for a different amp anyway, and then you will be back at square 1. Pick speakers first then match electronics second, is my opinion.