Using an old trick from my car stereo installers at the shop I work at, I determined that my left speaker was out of phase. The date on mine 1.29.2000. BTW here is the trick
Disconnect your speaker from the IO, take two small wire and connect them to the speaker. Take those wire and hold one to a AA battery, touch the other wire to the other end for just a second, repeat, watch the cone of the speaker. It should be going out and back to rest, or in and back to rest. Note the polarity of the battery vs the polarity of the speaker wires.
If speaker goes out and then back to rest and your + terminal of the battery is going to the + terminal on the speaker then it is in phase. If it goes in and then back to rest and the + terminal of the battery is on the + terminal of the speaker then it is out of phase.
Like I said I determined my Left speaker was out of phase