I'm still confused on how you have things wired. (which is likely my fault, not yours)

In the first post, you said they were connected to Front A / Front B. I have the 3808 and don't remember such an option. I took a look at the 4808 manual to see if there was a difference and while there are some different connection options for multi-zone playback, I don't see this specific option there either.

In your second post you said you have the second pair set up on "amp assign." In the 4808 manual, there is an option listed to have one set of front speakers designated for multi-channel listening, and a second set of speakers for direct/stereo modes. This allows you to have 4 front speakers, 2 of which are active depending on what mode you are in (surround versus stereo). The manual lists this option in the section having to do with bi-amping and bi-wiring your mains.

I can't find anywhere in the manual where they give the option of running both sets of main speakers at the same time. The only settings I know of on the 3808/4808 to run 4 speakers through 2 channels is on the Surround A / Surround B option, which I imagine they support since typical impedance of surround speakers is fairly high.

Can you elaborate on which channels you are using to run your 4 M80s and what mode you are listening in (or were listening in) that runs all 4 at the same time?

Epic 80-800: HG Cherry