I’ve owned some decent tube gear over the years (Cayin, Rogue, Allnic, Van Alstine) and some nearly high-end SS stuff (Coda, Pass, Mac etc.) I’ve also auditioned some of the very high-end brands. Admittedly, I don’t have much experience with low power SETs but I do believe I’ve heard some of the best of what push-pull tube gear has to offer.
IME, the Yamaha MOSFET-powered integrateds (specifically the previous 1100/2100/3000 series, not as much the current series) come closest to the tube sound than so many desire. This isn’t to say they’re slow and mushy, rather they have nicely saturated tones, a lush midrange and expansive soundstage. On top of that, the bass extension (of the 2100) competes with some of the beast SS amps over $10K. They sound far more powerful than their specs indicate (especially the 2100). The preamp sections in these integrateds are worth their original retail price alone IMO. I realize this all sounds like hyperbole, but when you actually compare these integrateds back-to-back with other amps costing multiples their retail price, they are hardly outclassed. Typically, what I find is that some of the much costlier amps do one or two things a little better, but none have outperformed the Yamaha’s in every metric. That includes comparisons between the Yamaha preamp sections and separate preamps around and under $6K. Twice now I’ve preferred the Yamaha preamp sections to stand-alone preamps approaching $6K, one of them tube (Allnic) and one SS. I won’t mention the latter one because I still need to sell it. 😉
While the various speakers I’ve used in these comparisons (Revel, Spendor, Stirling Broadcast, Spatial, KEF, Magnepan, Audio Physic) are considered “mid-fi” by the standards of this community, they are speakers that have mostly punched above or well above their respective price classes. And I’ve heard what far costlier speakers can do in good rooms, thus I believe I have a decent frame of reference.
With regard to push-pull tubes, I have found there are quite a few competive SS offerings in addition to these Yamahas, such as Coda and Pass Labs. But for around $2K on the pre-owned market, I think you’d be very hard pressed to do better than a Yammie 2100.
I think it’s also worth mentioning that I am relatively young among these parts and my audiogram tests show I still have excellent hearing. I don’t say that out of ageism. I merely believe it’s relevant because I know of multiple audiophiles who come on here and other sites espousing the sound quality of various components, then elsewhere they reluctantly admit they rely on hearing aids or suffer from tinnitus.
Good luck with your quest.