M4 has no sub-out, so I'm not sure I understand how a monitor can have it's driver moving forward while the attached sub to move its driver backwards. Also, RCA is connected to V+ and GND, so there's nothing inverted there.
I'll wait for @Daverz to reply here on how he can perceive this inverted polarity, so I can check it myself on my M4 as well. Thanks!
I'm running rca outs to subs and 1/4" outs to monitors, have to flip phase on subs.