Sharing my findings with attempts to raise output BJT current as promised.
I am running +/- 16V rails.
Using 255R in R38 and R39, I got around 186mv voltage drop on the output resistors (20R) when the amp is fully warmed up (160mV at cold start). That's around 9mA current. I could barely feel a temprature on the output transistors at this operating condition.
I finally settled on 301R in R38 and R39 which results in 250mV across the output resistors at cold start, rising to and stablize at 320mV after a few minutes. The output BJTs are quite warm to the touch but not hot. I am really liking the sound of the amp at this condition.
For what it's worth, here is a few other values of R38 and R39 I tried and the resulting voltage drop across the output resistors:
R38/R39 = 287R, 230mV cold start, 273mV warmed up
R38/R39 = 317R, 300mV cold start, 360mV warmed up
R38/R39 = 402R, 500mV cold start, did not wait for it to warm up.
This amp really sounds great on both my Senn. HD650 and LCD2. Subjectively the best among the headphone amps I own and heard.
Many thanks Kevin for your ingenuity and help!