Marshall made an amp back in the late 70s or early 80s called the 2000 series (no, not a DSL or TSL either) that ran 6 power tubes, had 2 channels (Super lead non master volume and a JCM 800 style Master Volume channel) that could be run seperately or combined...I had one, but sold it. Not a great sounding amp, but could be the basis of what you seek with some mods maybe, IF you can find one.