Well, in my opinion, though there are differnces between the triode and pentode modes in Decware amps, and push pull and single ended, they are not as represented in other manufacturers, but in fact differing windows from the same room. I find Decware push pull amps to be quite similar in sound to the triode single ended ones, so I would say that being locked into the idea of the "EL34 SET Class A signature" is in fact limiting oneself considerably.
I also feel that with the efficiency of your speakers (and I know there are other factors such as crossover type) you may well be able to get by with the Zen amps. And I must say, as wonderful as I've found the EL34 amps, the low powered SV83/EL84 amps actually have the potential to be the very best sounding of the Decware amps. The speed of the smaller tube in this circuit makes for amazing detail and soundstage. The EL34 amps I moved to because they offered more power that I needed (at the time speakers with about 91 db in a large room) and I listen to many different recordings, many of which don't sound that great, and in comparison to the SV83/EL84 amps the EL34 amps are a bit more forgiving and euphonic with lousy source recordings. In fact the SV83/EL84 amps may deliver what you're looking for in the EL34 amps. And when the SV83 tube is used, the Hazen Grid Mod is in effect. . . . These amps also have input gain adjustment and can be used without a preamp.
The "Select" is really an amp that no longer exists, which is now in improved form as the SE84ZS, which page is accessible via the catalog:
https://www.decware.com/newsite/SELECT.htmWhy it is not on the tube amp page, I don't know, the SE84ZSM Monoblocks also are only accessible via the catalog page. These amps CAN be run without a preamp quite capably. Preamps do add to the sound, and I had to divest myself of the "adding a preamp and interconnects to the system means sonic degradation" thinking. That may well be true of many makes and models, but not when using the Decware preamps such as the CSP2+ or the ZSTAGE (a reportedly excellent line stage preamp that is more affordable). These preamps really do contribute far more than you imagine you might lose. They're a cut above anything else I've used. If you look in the "articles" Steve writes about the use of a preamp, and I think also in the owner's manual or product page for the preamps.
The real best advice I can give you is to talk to Steve about your system, your room, your musical tastes and equipment tastes and let him advise you. NO ONE knows more about the amps and their implementation than Steve and his advice is SOLID. He's also one of the easiest persons on the planet to talk to. I recommend getting him on the phone when you can!