Hell, I have an o-scope and still set it by ear. Just turned the remote knob to max and put the radio about the loudest I'd listen to it (point right before any distortion is heard) then turned up the level untill it was at the right level with no distortion. That way I can turn the bass up/down with the remote knob without going higher than I should.

But I have a decent ear for fine tuning an EQ, most of my friends get me to tune their setups because they can never get it right...