The systems are different, but the sonic signature of an amp is rather easy to hear in a good system.
Are you talking about the Luxman m900u and the 10x? That was rather easy to hear with respect of the warmth of the amps. The speakers were Harbeth and Monitor Audio. Both were on the slightly warm side and not my preferred choices, but I adjusted to that. I am also going on memory of the m900u which I heard a few years ago with Harbeth. I almost bought the m900u. I did not because I did not think I could live with such as warm amp long-term.
If you are talking about the SimAudio 761 and the Luxman 10x that is a harder call since the Sim was playing on the brighter Paradigm Persona 9H which has powered bass drivers and really incredible DSP tuned base. I found the Luxman 10x warmer of the 2 and maybe a touch less detailed. However, the Persona is a detail monster and a bit bright; the Monitor Audio seemed a bit less detailed and warmer.
Given these system variables I am evaluating the Luxman and the Sim. My goal is to get a forever amp for my 2 systems. I already have the CODA #16 and evaluating other amps that are as good but sonically different. The Sim 761 is rather different from the #16. The Luxman is 10x not that much different.
I posted some more details on the Clarisys speakers that I heard at the shop that had the CH amp and the Luxman 10x. The Clarisys is a ribbon-based speaker that has some sonic resemblance to the RAAL 1995 Immanis headphone. I know the RAAL sound extremely well. So, the Clarisys demo gave me a good basis to compare with my #16 with the CH. I also own Magnepan LRS+ which the Clarisys also have some similarity too.
I have setup the RAAL headphones with my CODA #16 amp but that is not really relevant. The fact that they sounded sonically similar (maybe because of being ribbons) was the baseline. Not talking soundstage or imaging here.
I also get fatigued easy, which I found useful in evaluating gear. Funny thing is the worst demo (and most fatiguing) was with the Yamaha NS5000, the speaker I ended up buying and loving (I bought from another dealer).
On a side note, I am visiting my parents in Whitby, ON, Canada. There are 2 amazing hi-end stores cycling distance (10 min) on either side of town. I was able to sneak some audio listening sessions while visiting. I will be buying an amp from one of these Canadians if I get the Sim or Lux (almost certainly will).