It seems this is a common dilemma with those interested in the Luxman integrated amps, whether it be the 509/590 or the 505/550, few have heard both. I purchased the 590A II back in January and like you I am very pleased. Between the 509 and 590, functionally there are trade-offs both ways, such as, the 509 lacks a remote, this is a big deal to me; for the 590, as you state, it runs hot and for some 30 watts isn't enough, although it is a very powerful 30 watts. I was specifically looking to go Class A.
In talking with the dealer I purchased mine from and asking about the differences between the A and A/B units, he feels it depends on the speakers one uses.
In talking with the dealer I purchased mine from and asking about the differences between the A and A/B units, he feels it depends on the speakers one uses.