This process didn't work for my radio but perhaps it will work with a different Legacy HU:
"Key in ACC position, radio off: Hold preset button #6 while spinning the right adjust knob 4 or 5 notches; release button, then repeat. Now you're in the adjustable presets pages. Spinning the knob or hitting the "back" button will bring up loudness, EQ, and screen brightness settings, which can be toggled with the knob."
Maybe try it for the HK model?