@thriftyaudio given your existing investments so far, I like your plan for yourself on next steps. Since you indicated having just refreshed your PA-7 amp, go for it. Can’t think of a good reason not to try it with either unit you’ve narrowed it down to so far.
Fwiw, I normally run tube pre & mono amps on my main system. Late last year I picked up an older Pass/Forte amp, had it refreshed and upgraded. I’ve been listening to it swapping back and forth since. Channeling your own PA7 lineage that is. I like it well enough to keep it in play, and the tube gear has been sitting idle on the side. And as you know, some of this decision making also has to do with your speakers, but I can share without a doubt, a good preamplifier can really help the amplifier and your speakers to perform differently, hopefully better when you find a nice match and synergy.
As you may be aware, Darren Myers designed that Stellar Gold preamp before he left PS Audio to go join in at Parasound. I was eyeballing the internals and design on that unit, seems kind of like a unique and different design for PSA, lots of "other stuff", regulators, and discrete amplification stages fed by a big transformer in that unit. It might be worth a call over there to PSA to ask them what kind of serious demo they’d let you do, for 30-45 days, ensuring its a "good match" for you and your PA7 before committing to follow through on keeping it. Demo required imo!
Interested in hearing what they do for you. Would be nice to see PSA put their money where their mouth is on this one for you, if you decide to demo it. Best of Luck on whatever you decide.