Question for tube aficionados

I have a vintage Conrad-Johnson PV 11 preamp.
 I’ve always re-tubed it  with the cheapest tubes from Tube Depot (e.g. Electro-Harmonix 12AU7 and 12AX7, Sovtek 5751 and the like.). I’ve been very happy with the sound.
 My question is:
 Would it be worthwhile to spend more money on more exotic tubes?
  Would there be any appreciable difference in the sound?
 I’m powering the system with NuForce Reference 9 V3 monoblocks.
Hi RV,

First, I note the following statement in the manual for the PV11:

It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive auditioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11....

... Please note: The indiscriminate substitution of type 12AX7 tubes for the 5751 will seriously degrade the sonic performance of the unit.

Also, apparently four of the six tubes in the PV11 are used in its phono stage, and only two in its line stage. And I would not necessarily assume that a given tube is likely to exhibit similar behavior in the two kinds of applications.

Given all of that, it may be worthwhile contacting CJ and asking if they can tell you what tubes were originally used in the PV11.

Beyond that, FWIW like some of the others I have had fine results with Gold Lion reissue 12AX7 and 12AU7 tubes, in my case in line-level and driver stage applications in a Chinese-made Paxthon integrated amplifier I used for a while some years ago. They handily outperformed a number of vintage tubes I also tried in that amp, including some vintage Telefunkens which go for considerably higher prices.

Good luck. Best regards,
-- Al

Never sub a 12 type tube for a 6 type tube. The number is the voltage. Hence 12ax7 is 12 volts! BTW, a 5751 has 30% less gain than a 12AX7!
Thanks to everyone for their suggestions.

My speakers are modified Dalquist DQ 20’s.

Overall, the system is fairly well balanced.  What could be improved is occasional brightness in the treble, especially in the line stage.

 Ideally, I’d like to replace all six tubes, depending on the cost.