Would you mind elaborating on this a bit? I know it's not what you intended, but it kind of reads like they sound the same, which I can't imagine is true. What differences are you hearing? I ask because I've tried the Luxman in Tokyo before with HEK/Utopia and it was memorably great. But the 115V version in US goes for double the price of the 100V overseas so it discouraged me from buying one. I think some people buy the 100V and use a transformer, I don't know if that affects SQ. I want to try the P750u at some point though probably not at full US price..
Koven, I spent some time just moments ago comparing the two amps with the Susvara. I only have about 30 hours on the Susvara as I burn them in and I'm still getting a grip on their sound quality. That said, the 2 amps do sound different. It's not surprising that the Nirvana is warmer but the Luxman is by no means lean or cold. I think the Luxman sounds faster and has better control over the bass. The bass is really deep and tight with the P700u. It also has pinpoint imaging and layers within the soundstage are easily heard. They both throw a big soundstage and I'm really not sure which one is the winner for soundstaging. If I had to pick a winner based on this early impression, I would pick the Luxman by a hair. Ask me in a week and I may have a different opinion so take it with a grain of salt. The Susvara and P700u seem to have a special synergy together. All other headphones in my collection (Utopia, 4z, VO, Aeolus) I prefer the Nirvana by a small margin.
Regarding the Luxman price, I received a big discount on a brand new US market P700u about 4 years ago. I also got a big discount on the Nirvana.