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

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. 

I have the Pass Labs 30.8 amplifier (class A) and it sounds great for the pop and jazz music I listen to. If I listened to classical music I would probably own a tube amp. 

in all candor it’s always about the first watt quality. luxman and ref 75se have that in spades. then comes the mojo which they knock out of park. fwiw

I went yesterday and listened to the Luxman m900u amp and c900u preamp. The reason for this second visit to the dealer (Excel Audio in Newport Beach CA) was to determine if I needed to get the c900u preamp or if a lesser preamp with a DAC and room correction would work with the m900u amp. Something like the following preamp:

Anthem STR preamp
Linn SELEKT DSM
Lyngdorf 3400 (using only preamp section of integrated)

Long story short, I have changed my opinion of how to buy a system for my small room. Get the electronics before the speakers. The Luxman gear was so good that even with lesser speakers ($16K vs $5K) the sound was better with the Luxman.

I am even tempted to run the Luxman m900u + c900u with the KEF LS50’s I own if I cannot make a bigger speaker work without DSP. I was totally against using a monitor speaker because I wanted the bigger bass with the floor stander. However, that logic is out the window with the Luxman gear. Everything I played through them sounded special.