Alper,
In The Torii Mono manual, Steve warns that if KT-120 tubes are to be used, the amps must be re-biased.
I have rolled several pairs of KT-88 tubes in the Monos and am amazed at the different, sonic presentation of each of the pairs.
The pair that I always return to however, are the Gold Lion Special Edition KT-88 tubes, because their sound is the most transparent in my system.
Up to this point, I have had too much fun and listening pleasure to contemplate using a different tube such as the KT-120.
Take care, Mark.