If you are worried about inverting polarity in your system, the easiest place to fix it (if your pre doesn't have an invert polarity feature) is by changing your speaker cables... Wire + to - and - to +. Since each two polarity inversions will restore absolute polarity, you just need to correct once. Doing it at your speaker terminals is probably the least intrusive way of fixing the problem.
Then again, most people can't tell the difference. Including recording engineers, who can invert phase on recordings. Search for "woods effect" in the archives.
Then again, most people can't tell the difference. Including recording engineers, who can invert phase on recordings. Search for "woods effect" in the archives.