For all intents and purposes are the front and rear channel
outputs the same if the eq is zeroed?

Yes. The mp3 contains 2 channels of data, each is split into 2 (front and rear) and then fed through eq and fader.

So if there's no difference in equalizing front/back and no fading, then
front/rear should be identical (disregarding stuff like variance in components like caps, op-amps etc...)

Can't say I can visualize your set-up... Where's the amplification?

/Michael