All posts since Saturday are gone.

I replied yesterday, so...

...to repeat, you have a completely unused triode in the first 12AX7 (V1A; note the unused pins 1-3).  This half tube is used as as the first gain stage on on Channel 1 of a traditional 18-watter, which has been replaced with the EF86 channel.

This gives you an entire gain stage to use and play with.  A possibility would be to introduce an additional gain stage before the TMB preamp, that's how the "Hi" channel works on a JCM800.

You might as well do something with it, even if you wire the gain stage up in parallel (for a little thicker tone), otherwise you are buying for half a tube that isn't used.