Get good ones. I always feed my babies the best ! I would either get a set from ARC or a matched set.
It uses 4 6922 , personally with preamps I like to get matched pairs or quads so channel balance is as tight as possible. Pose the question here and other forums what the best replacement is. They probably used Sovtek during the period that was built. JJ makes a very good sounding 6922 and the Gold Lion 6922 is good too. The JJ has more meat on the bones and the EH is very good top to bottom, clear . I like the tone of JJ bettter but that is subjective