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

Current amp great soundstage but not exciting.
OP: I have the ref5se paired with a pass x250.5. Awesome details from arc matched with the fast and deep x250.5 - I am in heaven! I’ve pondered an all arc system - but fear it might be too clinical. 
Pass Labs, they are as good if not better than any amps in the price range.  You get a total package.  You will not regret your purchase.
I had the Pass 250.5 (not .8) with an ARC REF5 SE and sold it for a REF 75 which I still own. The ARC combo is the best I've heard in my room and I had a few high-end units over the years to compare (Bryston, Classe, Simaudio, Luxman, Pass Labs, etc). Synergy is critical and of course this is facilitated when components are coming from the same brand. I was skeptical initially about the relatively small power number of the ARC amp (75W) but it sounds as powerful as 200W SS amps I had in my room and does have the quality of tubes without the 'disadvantages' (very neutral sound not warm). It's a Stereophile class A if that can help :-) I highly recommend this ARC amp and I've read many times that it sounds better than its bigger brothers in the ARC line (could not confirm that myself though).  
For the enlightened, perceived abuse of another member is usually the reason why posts are called to the attention of moderators for removal. 
I find nothing wrong with a dealer or manufacturer making a contribution to a thread if they feel it’s warranted. Even if such posts might be perceived as blatant self-promotion, it’s up to the OP to evaluate the content of each post, as well as the reasons why such info might be discounted. Most here are adults, so I’m confident that everyone can discern the content of each post for what it’s worth.