Preamp tube

Another recommendation is to contact Brent Jesse (I'm only a customer), here's link to his webpage for 12ax7s , aside from his listing of what he has available he provides some views on the sound of different brands which you may find helpful regardless of who you buy from
http://www.audiotubes.com/12ax7.htm

I think I may have posted the same question twice on AG, sport about that. I’m getting great responses from both and I appreciate your input. How critical are the 12AT7/ECC81 to change? Is there a sonic benefit? The most I’m hearing are the AX7’s play the most critical part in voicing. WhT do you guys think?

Depends on the layout of the amp, which I'm not familiar with.  It all depends which tube or tubes handle input.  Similar tubes may be just phase inverters, so less crucial.  Mullard, Amperex Bugle Boy, and Telefunkun are all good but on spectrum, with ABB in the middle.

I’m sorry, what is ABB referring to?

ABB = Amperex Bugle Boy?

It's correct that rolling the 12AX7s will create a significant change in sonics.
According to the specs of your amp, the 12AT7's are the drivers for the power tubes. They increase the voltage from the preamp to the power tubes while also inverting phase. Rolling these tubes does have an audible effect on sonics, but the preamp stage will have a major impact on sonic signature.

Start with the 12AX's, then you can tweak the sound by rolling the AT's.