Best Tube Amp for High Sensitivity Speakers: 45, PX25, or 300B?

Thank you, Jerry.  You've effectively brought it back to the parameters of my original query.  I wanted to find answers to comparing low-watt valve systems and what the community thinks about these different valves.  I reduced the valve listing to three for a reason; I didn't just want everyone to tout their amps.  I already have a nice Swiss-Army valve amp.  I wanted to fine-tune the question to specific, high-end valves that render extraordinary clarity, dimensionality, breathtaking musicality, and live tangibility that the best valves can produce in conditions that can best employ them (high-sensitivity speakers). I lived in Europe (mostly Spain) for twenty years, studied production with the BBC under Queens College Cambridge, loved the British sound, and built a media company in Spain.  When I sold it all to return to the States, I hoped to one day reach that level of vicarious, tangible music listening that would exceed the most memorable moments in my past professional life.  This is my "end-game" system.  I am building a room just for it (as many here have done).  I am not as interested in thundering power as in palpable envelopment. Music takes me places, on journeys. For a special moment, I am with the creators and craftsmen as closely as possible. They are with me. There are special tubes that are sweeter, more sensitive to the nuances of music than others. I'm on that search for the right balance between dynamics, musical depth, and analog believability as many of us are. And like many of my forum compatriots, I don't want to poorly spend my precious investment on frustrating experiments and regrettable explorations.

Depending too your budget and type of musicyulike and speakers

Before I do that, I would love to consider several things:

#1 independent wired to the listening room. You might already did it! A great step IMO. If you like to go further, make it two. One for analog, and one for digital.

#2 clean power. EMI/RF problems sometimes are real problems for some people.

#3 room treatment. We, I mean, I listen to the room sounds first, then the other things in the system.

#4 like @audioman58 said. I sometimes like listening some classical, big sound stage, huge dynamic, etc. 300b or those 2w/8w amp really can get them there? I tried the "two years waiting" amp, I like it very much. But, some music want more.

Try something different like the 211 tube ,or 845   More then enough power and sound very nice 

https://caryaudio.com/products/cad-805rs/

a dedicated line yes awg 10 if possible , and as I did 4 wire one a common ground 

the other ground a isolated ground in its separate path connected to its own grid to ground more monies but worth it you don’t need to isolate the digital after this .

buy a very good Ethernet switch , depending on your budget the   SW8  only $600

or top of the line  innuos $3700. Depending on your dac and quality of your audio system  what you can afford , the AC outlets buy quality Gold over Copper Furutech  or another name brand ,even Pangea $100 AC outlet very good . And on router for sure a 12v minimum 4 amp Linear Power Supply , any gsrbage wall warts need to go $5 junk noise makers , little green computer sells for $299 and never use stock power cords ,at minimum on the LPS power supply a Pangea Sig MK2  for example  I even put a synergistic purple fuse in the LPS as well as the upgraded Ethernet switch , each one  small but important  improvements ,

and Ethernet cables cannot be low end or your streaming will suffer, this too applies to the USB cable. Everything counts , I am still working on upgrades  last 

your dac , to me as the source how much can you spend $$. Myself semi retired have to save for more expensive items , the T+A 200 dac  I still have a few months to go to save , is imo and many others dacs we have compared it to directly in our multi state audio get together for its $7200 price a true bargain it beats anything under $15 k and more and has HQ player built into the platform to give you the ability to find tune this to your audio system ,to make it better still. 

I think the OP is mistakenly ascribing personality to the 45, 2A3 and 300B valves. What matters more is the circuit design and parts used. I have a 45 SET custom-built by Will Vincent (autospec) on an ST70 chassis that turned out beautiful! Plus a Japanese Sanei SA-560A 2A3 SET made with Tango iron. This I won at an eBay auction from a Japanese seller. It is the quality of the whole amplifier - the gestalt - that elevates the performance rather than the specific tube type!