OP: Back when I was looking to change my integrated amp, I listened extensively to several McIntosh and Luxman models. On the McIntosh side of the house, I auditioned MA252, MA352 (at Magnolia), MA8000 at a local seller’s house, and MAC6700 at another seller’s. As for Luxman, I listened to 550AX and 590AXII (both class A up to a certain number of watts), and 507 and 509X (both class AB) at a dealer.
Personally, I preferred the Luxman sound, especially their class A models, and ended up buying the 590AXII. Compared to the McIntosh (at least the models I auditioned), the Luxman tilts towards neutral with just a hint of sweetness, is more transparent, better detail retrieval, has better higher frequency extension, and a slightly wider soundstage. I could hear more details and more instrument separation.
McIntosh had a more muscular sound, perhaps a touch too dark for my taste, but I felt that it had better presence in the mid bass area. I also liked the somewhat taller imaging and a more lush and full sound.
I will say that although I preferred the Luxman, but it was not by a huge margin by any means. Honestly, I could have been equally happy with the McIntosh.