Mainly because a VOG channel is not an official part of any home surround format, so it's something that has to be matrixed out, and there's just no way to know how well it'll work. I think 7.x.4 is probably as far as most rooms and systems can benefit from.
FWIW, I'll definitely be installing 4 Atmos speakers, in the ceiling. Probably RSLs, due to the great price. $500 for the four of them. I need to do some other modifications first. My HT room, which was finished in the early '70s has absolutely wretched looking surface mount fluorescent...
I didn't spell it out, but I was referring to surface mounting something like the SVS Elevation or ELAC Debut OW4.2, which are only a few inches thick and can be surface mounted to a ceiling as well as wall mounted.
As long as they are overhead, out in the room and not just high on the side walls, it makes no difference if they are surface mounted or in the ceiling.
is that your question?
In-ceiling should only be used for the Atmos speakers. So, the basic setup is, three in the front, then a 5.1 has two on the sides (not the rear) of the room at or a little behind the main sitting position. Those should be a couple feet above seated ear level. When you go to 7.1, you add two...
If you want Atmos, you definitely want some in-ceiling speakers. Be sure to locate them correctly. Then there’s usually side and rear surrounds.
I strongly suggest you get away from using Class A amps all the way around. Maybe you use one for the L&R, but that is a total waste for the rest...
To add to Dave, due to the center channel speaker, there's basically always an odd number of speakers, since all the others are added in pairs. That's why there tend to be a lot of 3, 5 and 7 channels amplifiers.