bias adjustment

bias target zone

without heatsinks: 15mA - 25mA
with heatsinks: 20mA - 50mA

don't set the bias above the recommended limits. the more bias current is flowing through the transistors the more heat they have to dissipate. You'll fry the transistors and destroy your buffer by over-biasing!
even with 32Ohms headphones at very high volume levels 20mA bias are enough to keep the buffer in classA
do the adjustments in small increments. The output transistors are BJTs which have strongly positive thermal coefficient, which means that as you increase the bias, the current through the transistors increase, and that will heat up the transistor and cause its DC current gain to go up, which would then in turn cause the current to further increase.
it would be best not to aim for your target bias right away, or else a few minutes later you'd find that the current had gone up significantly. Increase the bias slowly and in small steps, let the transistors warm up and settle at a stable current before making more adjustments. Do this with at least a couple of minutes wait time between each adjustment until you get to the target without drift.

before initial power up turn the bias-trimpots full turn left (counter-clockwise) for minimum resistance = minimum bias current
turn trimpot one turn right
measure bias voltage in mV (DC) across either output resistor: from TP1 to OUT or TP2 to OUT (sanity check: the voltage across either resistor should be the same give or take a few mV).
if voltage measures zero continue with right (clockwise) turns, you will probably have to do some turns until the bias suddenly kicks in
when the bias kicks in give the buffers a minute to warm up and settle, don't turn the pots any further unless the bias has become stable
carefully decrease (turn left = counter clockwise) or increase (turn right = clockwise) the bias by half turns until the target bias is reached. Wait a few minutes after every adjustment to give the buffer time to settle. With the temperature changing the bias current changes, too. Be patient while adjusting the bias.
fine adjust the last 5mV by quarter turns

before initial power up adjust the offset-trimpots to the center of their adjustment range (aprox. 12 turns from maximum/minimum)
measure the output offset in mV (DC) across an output-pin and ground (GND)
use the offset trimpot to set the output offset below 1mV

output resistor [Ω]	bias current [mA]	voltage across output resistor [mV]	power dissipation at idle [W]
2.2Ω output resistors (color code: red red)
2.2	15	33	0.050
2.2	20	44	0.088
2.2	25	55	0.138
2.2	30	66	0.198
2.2	35	77	0.270
2.2	40	88	0.352
2.2	45	99	0.446
2.2	50	110	0.550
2.7Ω output resistors (color code: red violet)
Ω	mA	mV	W
2.7	15	41	0.061
2.7	20	54	0.108
2.7	25	68	0.169
2.7	30	81	0.243
2.7	35	95	0.331
2.7	40	108	0.432
2.7	45	122	0.547
2.7	50	135	0.675
3.3Ω output resistors (color code: orange orange)
Ω	mA	mV	W
3.3	15	50	0.074
3.3	20	66	0.132
3.3	25	83	0.206
3.3	30	99	0.297
3.3	35	116	0.404
3.3	40	132	0.528
3.3	45	149	0.668
3.3	50	165	0.825
3.9Ω output resistors (color code: orange white)
Ω	mA	mV	W
3.9	15	59	0.088
3.9	20	78	0.156
3.9	25	98	0.244
3.9	30	117	0.351
3.9	35	137	0.478
3.9	40	156	0.624
3.9	45	176	0.790
3.9	50	195	0.975