Conrad Johnson ART Pre-Amp tube rolling

Hi, I just got used ART 1 through Audiogon, trying to figure out if there is any potential in rolling the tubes to experiment different favor and performance of the amp.

Anybody can enlighten what stock tubes CJ uses on this amp? What are other tubes I can try? There are 10 pcs of 6922, must we roll all tubes in one go?

Thanks.