Assuming the topology is similar to the Mk II, only the single central AU7 is a preamp tube. I believe the other 4 are drivers and inverters. No idea if that 5th needs to be in there--I wouldn't risk trying until you get confirmation (a call to Rogue?).
The KT-120 standard is Tung-Sol. I got a set of Genelex Gold Lion KT-88s, swopped them in, and after a while went back to the 120s. More... majesty. 88s perhaps a hint sweeter, but barely.