Which would you choose; Pass 250.8, arc 75SE or luxman m900u?

An owner endorsing gear they own is simply bias confirmation.

@celander   I get your point, but what do you recommend?

It's a journey for most of us that [hopefully] moves our understanding and knowledge forward. Sharing where one is, at that point in time, and the choices made along the way [for better or for worse] seems reasonable and fair. 

David, I simply recommend taking all the input to heart. And factor in bias to the extent possible. The closer the owner’s gear setup is to mine, the more I’m likely to weigh that contributor’s input favorably for the reasons set forth below.

Here is the problem as I see it. We all have different listening environments. We all have different gear setups, ranging from power conditioning (or not) to power cables to IC’s to gear and speaker cables (if needed for those not having active speakers, like I do for my ATC SCM20-2A’s which I love owing to their compactness) to speakers.

When I make posts to threads about specific gear, like I have about Jay’s Audio CDT2 MK2 transport on TeaJay’s thread, I list all the gear and accessories used in my opinion. Regrettably, the biggest factor, the acoustic space, is left out for obvious reasons.

@celander I agree. We need more of what you are recommending and much, much more shared (including additional context) so that those reading can make choices, with higher degrees of confidence and informed processing. Very Well Said. Thank you!

Without wanting to engage in regurgitated info already posted, the OP will ultimately want to select one or two of these amps for audition in his home system. All we can do is provide informed guidance to him.