It's hard to say without having detailed design information on the unit. However, in pro audio circles the phrase "limiter" denotes something completely different than a gain control or attenuator or potentiometer, and I would guess that is applicable here since there are level controls on the unit in addition to the limiter function.
What a "limiter" does is to smoothly reduce gain as the signal amplitude approaches some maximum permissible value. While a level control/gain control/attenuator/potentiometer applies the selected amount of attenuation to the signal regardless of the signal's amplitude.
So I would suggest leaving the limiter function at 100% and using the unit's level controls to reduce its gain. That may or may not have some side-effects, which you'll have to judge by listening, but I would imagine that they would be subtle at most, while the limiter function (if that is what it indeed as) would have side-effects that would not be subtle at all.
Fwiw, I found these specs on the unit:
http://www.accuphase.com/p-300_e.htm#Regards,
-- Al