I would like to join the others in thanking you for posting your very enjoyable YouTube videos. It was surprising for me to see that you came up with the same conclusion I did a number of years back questioning the need for a driver section in a single-ended tube amplifier if one will be using an active preamplifier. I too have been experimenting with this over the years and have made a few single-ended amplifiers without a driver stage. In most cases I did integrate a gain control for each channel on the amplifier to compensate for the difference in tube section gain found in most tubes. These controls are usual small screw-set potentiometers since the is no need for me to adjust them unless I notice a channel in-balance.
I am currently working on a project to easily compare 6L6, EL34, El37 output tubes as well as 12XX7 preamp tube utilizing a modified Chinese single-ended stereo tube amplifier that will allow me to quickly switch between two tubes using the same mono input to hear in real time the various tube differences. It is also useful in selecting the lowest noise preamplifier tubes for use in either the phono or the first preamp stage. I think it could also help in selecting the best phase inverter tube.
Thanks again to you Skunkie and all of the other Forum members.
Joe in Virginia