Preamp tube

Sylvania-Baldwin green label circa 1960’s is a nice sounding 12AX7. They can be had on ebay at reasonable prices!

Ampex or RCA .Pulls from Baldwin home organs are usually good  as well ,

 I use NOS Telefunkuns from the 1960's.  They are expensive but were a clear improvement over my existing tubes. 

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?

How critical are the 12AT7/ECC81 to change?

See your other thread. They will create a modest change in sonics.

Definitely swap out the Genelex for some NOS tubes. Choose a tube based on how you want to change the sound; eg, warm, neutral, more detail, larger soundstage.
Here is great info on tube brands and their sonic characteristics...

http://www.audiotubes.com/12ax7.htm