The Synergy 50 head uses a Push/Pull power amp section that is fixed bias, some refer to fixed bias as ("adjustable" bias)
Its kind of interesting a lot of the media hype speaks of Cathode biasing the preamps. 99% of all guitars amps preamp tubes use cathode biasing.
I think what the deal with Synergy is they use a real Cathode Follower stage to drive the tone stack if the original circuit used one, instead of the mosfet (Solid state) followers a lot of other module based preamps do. A cathode follower stage causes compression on 1/2 the wave length which results in a pleasing sound. Many Fender style circuits used Plate follower tone stacks and Marshal Style circuits are known for the Cathode follower tone stacks.