I had a C900f and now have an ARC Ref 6. I would never go back to Luxman. It is refined but way too soft and dull IMHO. I know it's all system dependent and YMMV but I find Pass (had 250.5 amp) and ARC much more transparent and 'accurate'. In term of resell value, I had a hard time selling it on used market and had to swallow a big drop in price. I have been very disappointed since prior to buying my Luxman preamp I had heard only good things about them. My dealer is no longer selling their products.I had similar experience with L505Ux, it was too soft for my liking and the vocal were suppressed, I used with Totem Model 1 and tried with Scansonic MB2.5 at dealer(during trade in)..
From a support standpoint, I had to contact Luxman for technical questions and despite many attempts to talk to them, I never got an answer. I heard similar complaints from dealers selling Luxman products. So it's only my -poor- experience dealing with them and others may have better stories to share but clearly I doubt it's the level of service you get from brands like Bryston or Pass Labs.
I did asked tried contact Luxman Japan and no response.
However I am using their Tube Power Tube amp MQ-88 which is far better than Solid state counterpart in terms of Vocal and clarity