Andy,are you talking about the internal output gain of the LP1, not sure if I ever found the access to it but will check again...
Hit the ALL buttonselect Master Level Hit Enter
set it to -1 ( at level 0 there's a strong likelihood of distortion as you build up tracks). then forget about it. Charles is of course right that it's nothing to do with impedance, and what you are experience is just a level matching issue. The LP1 is not an "instrument level device", it's a line level device which runs at what is usually called "consumer audio" level, some way between the old -10dB standard for consumer audio and the +4dB pro audio level which is standard in studios. Anyway, you seem to be sorted :-) andy