Pls help me decide Pass Labs X250.8 or Luxman M900u

Impedance is fine. 

I really appreciate all of the responses here!

I’ll update once I make my purchase and have the amp in my system. Will start to focus more on the Preamp now.

The Backert Rhumba Extreme really interests me- unless I can find a used VAC Signature MkII SE

I own M900u along with C900u. I also have Focal Sopra speakers that my friends told me would sound too bright with Luxman, mainly because of the beryllium tweeter. Room treatment is important as others have noted, but  in my book the front end and property matched cables are even more so. Bottom line: look at your system as a whole and not just the two mentioned components to see what will sound best to you. Try to work with a dealer that will allow you to work with multiple set ups until you are happy.

If you decide to look at the M900u, mating it with C900u may possibly be your best option, as they were designed to work together. 

Warmest, regards

The Backert Rhumba Extreme really interests me- unless I can find a used VAC Signature MkII SE

These two have different sonic signatures, so at this point it’d be good to ask what sound characteristics you’re looking for as that will make all the difference. Given what you’ve said about wanting to keep the upper detail of your D3s I’d skew to the Backert and also mention the Linear Tube Audio MicroZOTL or MZ3 preamp (depending on your connection needs). I’ll also reiterate my prior recommendation for checking out the reviews of both the Atma-Sphere and AGD GaN amps that are getting rave reviews as being a wonderful combination of tube goodness with solid state control and are upgradeable. Best of luck.

@garynospamm if you end up with Pass Labs amplifier, consider Audio Research Ref 5SE or Ref 6 in your price range. Audio Research tube preamps pair extremely well with Pass Labs amps. Speaking from personal experience.