Tube change.

As another owner of a Dennis Had amp (Inspire SEP Firebottle HO...high output!) I do sympathize with multi tube amp owners (owned a Jolida amp for a while that had 4 output tubes). I'm obligated to use efficient speakers but I like horns so it's FINE. The cool thing for me is my preamp uses 6SN7GTB tubes as well as the Had amp so various versions of those accumulate in my tube drawer as well as the Had power tube heap. I like Gold Lion stuff mostly and think their KT88s are great...as well as the 77s, 66s, 120s...you get the picture. It's almost too easy to take the 2 minutes or so roll 2 tubes (preamp tube is an Amperex that's likely a rebranded GE...NOS GEs are preferred in the preamp). I swap the Had with a Pass XA-25 when the mood strikes me so there's that.

Is your pre-amplifier tube or solid state? If it has any tubes i recommend focusing on those as they are the beginning of the food chain.

I upgraded older tubes on a preamplifier which had two tubes to Amperex Orange pq red tip. After making this change i did not feel there was a need to change out 16 power tubes on my monos.  these tubes were on the pricey side but a lot cheaper than replacing 16 Power tubes.  

Gold Lion KT88s here in C-Js best amps.  on my second set.  They recommend them.

I am not big on buying into Output Tubes, but have bought into such Tube Types recently as a result of having to.

I am with the Camp that believes the end of the signal being the betterment over what comes before is getting the wrong end of the stick.

The Sent Signal is everything, do ones best that they know how to, with the intent to provide what is to be met downstream the very best that is available within a constraint of a budget.

Small Input Tubes and Output Tunes in advance of any Power Amp Output Tube is where to focus the available funds. Only concern oneself about the Power Outputs when they are losing their MoJo and moved nearer the non-ideal spec's for the Valves.

Then if one wants to dent their coffer, why not money is needing to be spent, so why not on something that costs more, but comes with the notion, it is to be quite special. Hopefully all the other choices made, bring the true symbiotic relationship between the overall selection of Valves.