Auro 3D is 5.1 or 7.1 + height speakers for all channels + VoG speaker above you.

Think of it as three layers: traditional surround + height + from the sky.

I've read the Dolby to Auro 3D upmixer works quite well. As for the selection of native Auro 3D material, I'm not sure.

As for M2s, you know I love them in my 2.2 living room. For home theater, I've become a believer in full channel audio from each speaker. Every speaker needs a co-resident sub...LOL!

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated