According to the schematics the VT 100 MKII is a fully balanced design. The offset between pos and neg branch needs to be set to 0 and that's taken care of by some ss circuits between the 6922 (some adj. can be made with RV1/RV2 trim pots).
The 6922 are double triodes and it's of course harder to match those tubes because you need a lot of them in order to find 4 tubes per channel where the two triodes in each tube are also about the same quiescent current. That makes it time consuming and expensive. In general Audio Research biases their output tubes very hot and they need a lot of tubes to select from in order to reach those goals. That's why it is so expensive if you go to Audio Research for retubing.
Many things can go wrong if one tries to do this buying tubes (even matched) somewhere else unless one fully understands how this amps work. Schematics are available online.
To use the VT100 only makes sense IMO(considering the high cost) if one uses a fully balanced system (at least preamp to amp).