Determining polarity? and Modulus3A question also

I wonder if one can tell using a multimeter if their speaker leads are in correct polarity. I know with my Modulus pre-amp I am supposed to switch the cable polarity to make up for the preamp being inverted and at this point I cant tell an audible difference when I switch them.How would I do it with a meter?
Another question is about the gain in the Modulus 3A. The notches on the volume control are big steps for my Klipsch La Scalas with CD source. In the manual they mention older models had a dip switch to tone it down but then they deleted that to improve sound quality. Can I add something to the circuit to lower the incermental gain?