I have a Luxman 507 (no prefixes or suffixes), one of Luxman's first transistor amps, from 1974 ('78?), I believe. I use it to drive Yamaha NS1000x speakers, which are truly top-notch. My CD player is an Ah! Njoe Tjoeb CD4000, also truly tops.
We (wife and I) really like the sound of this system in our main room, which has soft floors (tatamis), wood on all sides, and lots of cloth - more absorbers than reflectors. The sound is clear and very detailed, yet warm and well-balanced, and has deep imagining and realistic coloration and separation of each instrument. It sounds to me more like a high-end tube amp than a transistor amp in many respects. We listen to an extremely broad spectrum of music, but not at extremely high sound volume.
But as the Luxman was very inexpensive (at about USD500), and is a bit dinged-up, I've always felt I could improve on it and have been trying different amps on loan from the (super-good) local used stereo shop for many months.
I've tested it against several "higher-end" amps, including Accuphase, Krell, McIntosh, and other Luxmans, and so far this old 507 bugger still sits on the throne. Let me know if you'd like my comments on any of those comparisons.
Right now I'm testing/comparing it against a Primaluna Prologue 2, which images well and offers rich, full sound across the spectrum, but with my setup and environment is not better than the old Luxman in any sound respect except perhaps bass volume, for which the Luxman has a knob to turn up when I want more bass. Through the crystal-clear NS1000x's, the harmonic distortion of the Primaluna is too obvious and changes the coloration of all instruments too much, while everything has a sandy, grainy quality characteristic of tube amps, but this is just too obvious. I also have an old pair of low-level Rogers speakers (LS-2a) that the Primaluna sounds pretty good good through, though, but the NS10000x's are my main babes, so I will give the Primaluna back to the shop, even though it's so pretty to look at.
Here in Japan, the local stereophiles generally prefer the original Luxman SQ38 (various suffixes) - types as for Luxman amps. Whenever looking at Luxmans, someone here is always sure to tell me not to even consider anything pre-1984.
As a Luxman owner, I just thought I'd add my two Yen to this thread.