Good question, but the VR MINI did not have enough continuous output current (especially not enough for a pair of 2A3 or SV811s).
Another thing that I have learned is that a floating supply for the filaments (like a battery, or isolated ultracap bank)
is not the best thing in terms of hum pick up. Sure, the power itself is very clean, but it's a LOT more complicated with that
in terms of picking up 50/60Hz noise fields with the sensitive direct heated triode tubes themselves.
With the L2 Preamplifier circuit, the way that I am referencing certain parts of the circuit to AC Ground and with the mesh tube covers in place (they also get tied to AC ground), there is no hum with any of the DHT tubes that I have tried! It makes a big difference! Certain tubes that I gave up on in the LIO DHT PRE (e.g. Psvane WE205-D Western Electric Replica) due to excessive hum are quiet in the L2 Preamp. And the one switch filament selection on the back panel makes rolling tubes of different DHT families much easier.
Anything to squeeze the last ounce of goodness out of the already superb LIO DHT!
I'm investigating and highly considering things for LIO in 2019 - but I just can't go into any of it yet. Sorry.
In the meantime, keep those DHT tube sockets clean and tight - and enjoy it!