The Ref 75 shipped with KT120 tubes and the 75se uses KT 159 tubes. But you can use KT 150 tubes in the Ref 75. Like all the fairly recent ARC amps that have vertical tubes.
I am not that familiar with your speakers. But I have a feeling something like the Ref 150 will sound a little more open with more well defined base My Elipsa SE speakers are rated at 91 db sensitivity and minimum 50 wpc. I preferred the Ref 150 to the 75. But the only real way to know for sure is to try them in your system.
I had 2 systems. I sold a Ref 2 mk2 to upgrade to a Ref 3. Then the deal for the Ref 3 fell through. I put the LS 25 mk2 from my other system in the main room while I looked for a new preamp. After not being impressed with a demo LS 27. I took home
a demo Ref 5se for the weekend. The next Tuesday morning I called my dealer and told him I did not want to return the Ref 5se. How much would
he
sell it to me for. The Ref 5se was that good I did not want to let it out of my system. I had to also sell my beloved LS 25 mk2 to afford the Ref 5se. So now I only have the main system.
If you have to compromise, I would compromise a bit on the amp. You can always upgrade later. The preamp will have more of an impact on your system. Used the Ref 5se is a real bargain. It is just an incredible oreamp. It is easily twice as good as the LS 27.
I also own a DAC8. I am thinking of moving from a computer to an Aurender streamer. Maybe one with a build in DAC. The DAC8 or DAC9 for that matter does not work that well with
Aurender (or Moon) streamers. The nice thing about the
Aurender is that it has a 2 TB hard drive so you don't need a computer. You can just copy your music files to the hard drive.
The DAC8 requires software which does not seem to be one of ARC's strong suites. I also own a Ref CD7. The Ref CD7 is very noticeably better than the same CD ripped and played with a computer through my DAC8. The DAC8 sounds best through AES and worst with USB.
You may want to browse
AudioAficionado.org They have an Audio Research section, B&W section and many other manufacturer specific sections.