@georghifi --
All else being equal for current delivery into low impedances (power supply etc), I would go the Luxman for bipolar outputs as they aren’t phased by low impedance speakers and current delivery as much as mosfets are.
I don’t know about Pass Labs, but I agree with you that the Luxman has no problem driving my Sonus Faber Olympica II’s which are 88db and 4 ohms. It doesn’t even break a sweat and never sounds as if it’s trying hard. But I guess the real question is does bipolar sound better than mosfets at reasonable volumes?
Also, I see people comparing the Luxman 509 with Coda and Pass Labs. IMO, the right comparison should be between the 590AXII and Coda or Pass Labs. When I first heard the 509 and 590 side by side, I couldn’t tell much of a difference, but after living with the 590 for a few months, I went back to the dealer this morning (trying to sell some stuff on consignment due to unexpected expenses) and asked him to play the 509 for me again. The difference is very obvious now. The 509 is more dynamic and the bass is tighter, but it lacks the sweetness and effortlessness of the 590. I could immediately tell that piano, saxophone, and horns sound more natural and fleshed out on the 590. Also, there is more immediacy when it comes to vocals.
Anyways, as you can see here, no one is offering their opinions based on actual ownership experience between the two specific models the OP asked about.