Thank you so much for your insights PB!
I'll wait to hear from PJ about the transformer, but it sounds very promising!
The speakers are definitely a factor in the highs. They are full range speakers, so the resolution in the highs have some limitations. With a stock Stereomour, the Omegas were bright but not airy, which I translate to lacking energy above 10K or so. However in measurements (into an 9 ohm non inductive load) I only see a 1 dB drop in output power at 20 KHz.
Regarding the delayed start, I have been using Sovtek 2A3s as stock. I had one die on me because it was arcing on power up. I thought that maybe a delayed start might help with that. But if that's not useful I would so rather leave it alone. I haven't tube rolled because tubes are $$$ these days.
Regarding the LED biasing of the 2A3s, it appears that I need to get 60V at the cathode (I measured 58 V). As a beginner, I thought I could just get that voltage using LEDs. I would love to hear more why you don't recommend it. Noisy? Or just stupid? If it's noisy, I might be able to add a PNP pass transistor? Maybe 50 mA is too high, although the HLMP 6000 has a max forward current of 90 mA. But with a forward voltage of 1.6V that would require 37 LEDs in series. Maybe that's just dumb. The Stereomour would look like one of those rice rockets from the 90's with under carriage lighting.
Regarding biasing of the driver tube, For the 5670, I was thinking about using a 270 ohm resistor in place of the LM431, which would bias the grid at -1V keeping the 3.6 mA current source. I didn't think about using an LED.
I'd like to ask one more question if I may. I saw on the Stereomour II forum that someone replaced the output transformer with a Kaiju one. I asked Eileen about it and she warned me that the Kaiju iron was not designed for the Stereomour. I measured the impedance ratio of the Stereomour to be around 560 so an 8 ohm load would appear as 4500 ohms at the primary (I think that is why the transformer is labelled 4K). Is the important design parameter the plate resistance (800 ohms for the 2A3 and 700 ohms for the 300b)??
There's the parafeed inductor, which I frankly don't understand how to choose. Maybe that won't work on the 2A3 at all. There's also the issue of whether the Kaiju iron would physically fit where the Stereomour iron is (I also have the Triad C-7X stacked atop the parafeed choke).
Thanks again for your insights!