BMK2 used in cathode-biased amp

[Champ81]

Initially I wanted to have an adjustable cathode bias to balance the hum. And that was achieved.  I am and was still new to this idea of biasing amplifiers but still learning. From what I gather now the adjustable cathode bias is varying potential difference between the grid and cathode. In a fixed bias amp its varying the potential difference between the grid and ground.  This was new to me.

Would it be worth it to convert this completely to a fixed bias amplifier. Tonally would this make any difference? Also because a fixed bias amp is referenced to ground you could also vary the current draw without the push pull configuration. Am I correct in saying this?