Which qualities did you find with the tube amplifiers that lead you on the search given that you already have the highly regarded Pass Labs.
This is an interesting list of amplifiers that you've narrowed down to. I'm not familiar with the Supratek Malbecs, but I have heard the parallell triode Merlot and must say that I was very impressed with them. At the time I was looking for more power to drive the panels of my ReQuests and the Merlot was a bit low on the power. Mick did offer a Merlot-based custom made, push-pull triode amplifier based on the 6C33 tubes but I did not have room for 4-piece system. If I'm not mistaken, the rest of the amplifiers are all push-pull, ultra-linear design. May I ask the rationale for this list? There are other worthy amplifiers you should consider on this list: Cary 805C Anniversary, VAC 70/70 Renaissance, Canary Audio, Cary V12R, BAT vk75SE... to name a few. Given the Summits with the internal bass amplifiers, you don't need a whole lot of power, but you do need clean, high-quality power for the panels. I found that around 50-70 watts per channel being the sweet spot, balancing the simple circuitry in order to stay close to the original signal, and having enough power for the panels.
I my case, I favor triode design for the full-midrange performance, and I found that the Cary V12R (AES SixPacs) work well in my system. Others have good success with Cary 805C and VAC Renaissance as well.
Good Luck