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
I sold the Belles. They were definitely not compatible and were not powerful enough to drive my system.
The NuForce are much stronger, and they sound fabulous.
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?