I haven't contributed in some time, but I have been trying to follow.
I have heard some seriously good systems and components. I can tell you that the REF 10 pre-amp is one of the absolutely best, period. In my humble opinion, it would be a serious mistake to get rid of it. There are some out there that would compare, but not jaw dropping. The REF 10 is just outstanding.
I haven't seen lately whether you have taken the dive into phono yet. Once you nail down your basic system (laugher), it would be outstanding if you could then go the phono route.
Not long ago, I ventured to Optimal Enchantment in Santa Monica and listened to Randall's house system. Vandersteen 7 speakers, with Audio Research REF 10 Phono stage, REF 10 pre-amp, REF 250 SE amps and stupidly expensive Basis turntable, arm and cartridge, with top audioquest cabling. I have listened for decades to wonderful systems and this was the very first time that the system completely disappeared. I've never experienced that before. I know you said that you tried another Audio Research tube amp, but if you haven't tried the REF250 SE, you've missed out. in my opinion. The other amp isn't in the same league as the REF250SE, and the combination of the REF 10 pre-amp with the REF 250SEis simply stunning.
Also, I tried to go back and discover what speakers you are using. I saw mention of Martin Logan 15a. Is this correct?
continue having fun. Your efforts are not only fun for some of us, but very informative. Direct A/B comparisons in the same system is absolutely the way to accurately compare and chose equipment. But, although Randall would probably let me take equipment home to listen, I haven't asked yet, only Stereo Design in San Diego actually routinely let me shlep heavy, expensive equipment back and forth from San Diego to LA to listen. Unfortunately, after over 40 years, Steve called it quits and Stereo Design B&M store is closed.
enjoy