I've had a 300B amp (western Electric tubes) and liked it very much, but there are certain things single ended tubes do really well and certain things they just don't do well. If one is about overtones, harmonic purity, micro dynamics, etc. and listens for involvement, they're great. If you love music for the "energy", you notice some issues.
I find the volt+ family to appeal to the sort of listener who's into music reproduction at the "refinement" end. I thought Poultrygeist's very good review of the Volt+D to be very much a description of the same amp I've been listening to. I agree about the strengths. There are serious listeners who don't like the highs in class D and the TI data sheet for the TPA 3116 does show a jump in the distortion levels at 6-7 K. My upper range hearing's probably deteriorated a lot, so I'm a bad judge of upper level overtones and the like.
I do think there will be a lot of listeners who find that going over to the tpa325x is a no brainer. Like the 300B, the things the Volt+D is good at, it's really good at. fwiw, I think most any solid state amp will have more bass than a single ended 300B. I think the extra power, lower measured distortion, of the tpa325x results in a more relaxed presentation , particularly with conventional speakers like mine. I still can't compare how the 325X does with the stuff the Volt+ family does so well. To my ear, they're quite different. One is "listen to" and the other is a bit more "listen into".
Over the years, I have found one thing that's very telling. At some point, you stop playing audiophile and just listen. I notice with certain components, I'll start listening to particular kinds of music a lot more and avoiding certain other types. There are components that sound quite good to me when I'm playing audiophile, but I'll notice that I stop listening to music much at all over time (happened with one of the hifimeidy tp2050 amps). If I find myself listening to a broad range of music and listening a lot, it's the most telling sign about how well it's aiding in the reproduction of music. With this sort of stuff, my best judgments happen when I turn off my attempts to consciously critique, judge, analyze and just see if I can love the music.