What input cascode? I don't see no stinkin' cascode, but a simple input triode followed by a impedance reducer (AKA "cathode follower").
And... what's up with running these tubes substantially below their nominal current range? Extra gain? More exquisite sound stage and detailed separation of challenging mids? Brilliance on the cymbal-range, and power bass? [i.e. audiophile weaselwords...]
Run 'em where they're supposed to be, and they'll reward you with great response, and remarkably long life. The "problem" with the M7 circuit, all its reputation (and silliness with doubled-up resistors) notwithstanding, is that it also is a signal inverter. The phase of its output is reversed from the input.
While it "shouldn't" affect the acoustics of its result (because the Fourier Transform Theorem says that the power-spectrum of the frequencies of a signal A(t) are exactly the same as its inverse, -A(t) ...) in actual listening, it does. Entirely at the low-end of the frequency spectrum, where our ears are sensitive to phase. Mids? Maybe some ears can discern phase inversion from 200 Hz to 2000 Hz ... but not many. Me, no. Above 2000 Hz, no one apparently has particular phase sensitivity. Below 200 Hz, many people do.
Well... that's why there are those lovely reversible speaker cables with banana-plug jacks. Wait, what? We don't use 'em any more? Well that's sad!
Myself, I'd use a pair of tubes for each channel. An input amplifier through a cascode constant-voltage section (running about 100 V plate), and another identical section to amplify the signal again, cascode on the plate running 100V. Of course the 2nd stage couldn't be exactly identical 'cuz there would be too much voltage swing for its cathode. So... use the resistor-resistor lifter to tame things. Still, gain would be decent, and the output waveforms would be nice and symmetric, with semi-nulled triode transconductance being the amplifying technology.
Stick that on your sound stage and smoke it!
GoatGuy