Nothing (AT ALL) wrong with the above, but: here's another tack, you might consider.
You already have two excellent amps, that are a better match to your less-than-efficient speakers, than tube power would be. Even with the powered sub.
Either would easily prove transparent enough to convey whatever improvements made, in your preamp.
The Paragon System E (NICE pre, btw) was built with MOSTLY Metalized Mylar caps, which are good (basically) for ever.
The external power supply is a huge plus, far as noise reduction.
BUT: if yours has the two, light blue, electrolytic caps; they are over forty years old and could (probably) use replacement. As well as any electrolytics in the PS.
Older components can still sound good with aged/weakened electrolytic caps, but: much better, if refreshed.
Whether you choose to address those or not: why not explore the world of 12AX7s extant, to shape your system's sound, to better suit your aural palette?
Were you to purchase just one pair of NOS 12AX7/ECC83/5751s: there are three positions per channel, in which you could try them. (great flexibility).
ie:
For a warmer presentation: British tubes (ie: Mullard or Brimar).
Clear as crystal: Telefunken or Seimens.
Somewhere between those: Bugle Boy, Amperex and some USA (RCA, Sylvania).
Of course, you'd want to be certain; given their intended purpose (your pre/phono), they were tested for the lowest noise possible.
Brent Jessee* would be my go-to, far as MY preferential/most trusted source.
Here's a bit of wisdom, from a popular 6SN7 comparison, that's applicable to any tube circuitry, using multiples of the same tube:
"One thing became clear based on customer feedback, combining 6SN7 types seems to work better than using all 6SN7s of the same type.
With so many preamps and amps using this tube, you can end up with
Six 6SN7s per channel.
It appears combining tubes like the VT-231s as voltage amplifiers and 6SN7Ws or 6SNGTA/GTBs as driver tubes you gain the strengths of all. Using one type seems to accentuate the tube’s weaknesses."
*http://www.audiotubes.com/12ax7.htm
(Brent's on vacation until Aug 6)
Have fun and happy listening!