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.
128x128rvpiano
Modified Dalquist DQ 20’s.
The Belles just didn’t push them hard enough for impact.

Interesting.  The figures in this review suggest an average-ish impedance curve.

http://www.hifi-classic.net/review/dahlquist-dq-20-243.html

Did the modifications make them harder to drive?

Could be.
 The bass response is far better than the original was.
Really quite impressive!

The main thing, though, is that it just sounds better with the NuForce.
Objective evaluation of improvements in a stereo system is hard to arrive at.  There are so many subjective factors involved.  So I pulled out the Chesky “Ultimate Demonstration” disc that I had listened to prior to tube and amplifier changes. This is a very demanding disc which revealed severe limitations in my old system in just about every area.
Listening to it again now, I found the system to pass most of the tests very well. Of course, you could say there’s at least some degree of subjectivity involved here, too.  But, at least it’s somewhat objective.
RV, I was really lost about the Belles ,my 150a Reference VII has no problem driving my 4ohm , 87db Totem Sig Ones which are hard  to drive .
Knew nothing about the DQ 20's . Worked internet , 4-5 reviews all noted how hard it is to drive, several said hardest speaker to drive they had ever encountered .
One said 250 watts a side was bare minimum , 400 would be better, guessed its to be a 82db load .