Trying to decide between 2 Nagra classic, single boulder 1161, or Luxman M10-x

First of all congrats on the new speakers. Those are special. Second of all, your Pass X250.5 is no slouch. I don't know what exactly you dislike about the combo, but that amp is not a dog by any means. Maybe give it a chance if you haven't already.

I owned that Luxman M10x for several years and it was very enjoyable. I would not hesitate to recommend that amp to anyone. I eventually switched to speakers that are easier to drive and swapped amps for a set of Pass Labs XA60.8. My former Vivid Audio B1 speakers sounded much better with the Luxman, and my newer Duevel Bella Lunas prefer the Pass XA60.8, which shows how important it is to properly match the amp and speakers. All the amps you mentioned are likely great in their own ways so it comes down to pairing and preferences.

You may already know this, but Boulder is replacing the 1161 with a new model, the 1162. If it’s not available yet, it will be very shortly.
you may want to wait but if you don’t, the 1161 is a great amp.

you should insist on a really good price because it is no longer a current version and that’s worth something

Thank you everyone.  I pulled a 180 and bought a D'agostino momentum S250 after a final audition! Very excited!