Newb Tube question

I moved from NAD PP2 to the ProJect Tube Box DS.  I would imagine the sound is similar to your model.  That move was dramatic in my system.  I have Audio Research amps and preamp so later upgraded to the PH5 which was another wonderful leap in sound.  It seems we are similar that we simply love what the tubes offer...in general.  I have had minimal experience with tube rolling and have not been able to distinguish or see any appreciable differences.  You have options for a minimal investment so I would encourage you to look at a different mfg tube.  You get into the NOS realm and you can easily spend more on a pair of tubes than you did on the preamp.  I feel it would be a better investment to upgrade the component to whatever brand preamp speaks to you.  Shop the used market and you can always resell if you don't like it.

Having recently acquired a Pro Ject Tube Box S2 phono stage,

I'm liking what I hear

and am wanting to learn more about tubes.

No no no, it's a bottomless well, stick with whatever you already like, sleep like a newborn baby.

Your 65 year old ears will be able to hear the difference if you're a critical listener.  I'm 63 and have significant hearing loss (so I listen at an elevated volume) and I am able to hear things I would never have believed, and it's because I'm a critical listener.  When I listen, I sit in the sweet spot in a dark listening room so I'm not distracted by anything.  My attention is focused on the music, i.e., there are never any other thoughts running around in my mind, I'm totally fixated on the music.  My listening pleasure comes from, as an example, hearing every nuanced expression in Etta James' voice (in my opinion that woman's vocal chords are connected directly to her heart).  During one listening session, I heard something change in her voice and became worried there was something wrong with my audio gear.  (FYI:  IF I had been listening to the music as "background" music I never would have noticed a change in her voice.)  I put on a CD designed to "break in" audio gear and selected the track with a frequency sweep form 20Hz to 20kHz.  As the pitch began to climb I heard a very slight "rattle" coming from behind my speakers at around 400Hz.  I walked back there to find I had placed the steel top plates of my mono bloc amps (which I had removed for additional cooling) leaning against the wall on top of each other.  As the frequency swept through 400Hz they began to softly rattle and then stopped as the pitch continued to climb.  I laid them flat on the carpet, put Etta James back on and was totally relieved when her reproduced voice was back to normal.  I'll give you an example of what critical listening is for me.  A friend asks you (or me) to take a ride with them in their car to help them identify a noise they hear.  After driving around for 20 minutes listening to your friend say "it's kind of like a chirping sound coming from the front right tire", you finally hear it.  Now you're trained to hear it, and each and every time you get in your friends car you hear the sound without effort.  So how is that like critical listening?  The by-product of sitting in the sweet spot and listening to every nuance of the music is that the "training" happens naturally.  Once you're used to listening to the detailed expressions of a female vocalist (for example) it comes without effort each time you sit down to listen.  My point in all this is that the "training" I'm referring to happens even if there is significant hearing loss, as in my case.  Are there things I can't hear?  Undoubtedly, but I can easily hear the difference between audio electronics, and, if you're a critical listener, you'll be able to as well.

+1 for Brent Jessee http://www.audiotubes.com or Kevin Deal at Upscale Audio.

Brent Jessee has a good description of the general characteristics of various tubes that I found helpful

I am about your age and a relatively recent tube-a-holic!  I think I love them because some are older than I or at least the correct generation.  I found the following write up / review to be very helpful although I do not agree in any way with his blanket indictment of 12AX7 tubes...having run them all I have some favorites.  I also found Brent Jesse's website to be a great wealth of information.  Have fun and enjoy the journey!

https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html