Grappling with the complexity of the latest suround sound options, Atmos, etc.

And ignoring domestic limitations and technical interfaces...

If one is starting from a convention 5.1 DD/DTS capable cinema installation (Fl, FR, C, Sub, RL, RR), which additonal speakers are most important to getting the effects of Dolby Atmos material, and is their positional allocation consistent with DD/DTS installations?

Are the various extra overhead effects speakers even necessary or is the sound quality in 5.1 good enough to show what Atmos can do?

The Atmos setup (based on reading a sample User Manual from Marantz for their Cinema 50 product) seems to emphasise the side positioning of the surround speakers, whilst I have run my rears (in a 5.1 setup) from the "rear" output of the processor. Is this an important difference and one which should be resolved by repositioning my rears to the side for Atmos?

And the side/rear conundrum introduces another variable. Should the sides or rears be the more capable speaker?

Thanks in advance for your collective wisdom.

In the spirit of Spinaltap, I would like to confirm that I am not involved in the corrupt theft of a global sport.