I like the above circuit.
This is more in line with my idea of driving with OpAmp's.
This way I can apply the ideas in this sheet about offsets to zeroing the tube etc.
Edit: this pdf also drives with PWM in figure 2 ....
Trouble is the arduino's don't have enough PWM outputs.
This schematic from your posted pdf is exactly the way I was suggesting the current generator transistors should be driven with an opamp. This will allow you to control the ionizing current to the n th degree.
From what I have seen so far, you should be able to lead the way with absolute precision control of the CC tube current using a micro and the circuit would should be relatively simple too.