The two 10 ohm 10 watt resistors act as amplifier loads to protect the output tubes and transformers when the headset is in use and the internal A-100 speakers are switched off.

The 2.2 ohm resistors were probably chosen for use with the 4 ohm headsets mentioned on the two page attachment I sent. Two 15 ohm resistors will probably match today's newer stereo headsets that are usually 16 to 32 ohms.

If the sound is too shrill because the headsets are too wide-range, try connecting a plastic 0.5 uF or a 1.0 uf cap rated at 50 to 100 volts [available at R/S or any electronic parts store] across the Left and Right headset jack contacts where the two 2.2 ohm resistors connect.

Choose the cap that rolls off the highs best to your liking. I think a 0.5uF or a 0.47uF will probably be about right, but if the sound is still too shrill, try a 1.0 uF cap. These are plastic caps, not electrolytics. The caps R/S sells are usually blue in color.

The cap will roll off the highs coming from the AO-39. The reverb signal is already rolled off because of the signal processing in the reverb amp.