Some nice cascode properties: very low input capacitance. THe lower device is screened by the upper, and it ( globally ) is acting as a buffer/source follower.

Instead of rigging the lower gate to the current set resistor( as in a CCS ), it is the input from the volume control. Current is regulated by a full-circuit CCS on a negative rail. +/- 25 volts should be adequate.

5-10 uF of coupling cap, and at low voltage.

Always wandered what a good L-C filter in a SS amp's power supply would do. Of course, we'll need two of them for the bi-polar rails.

Of course, we'll do rectification with vacuum diodes, preferably IDH cathodes, like 6AX4's.

The trouble is that my sleeve of DN2540N5 MOSFET's dissappeared in my move....:( along with my coffee can full of salvaged photo flash caps from disposable cameras.
regards,
Douglas