Thanks for this, especially the tip about preouts to the A90. I quite like the idea of being able to preserve what I have now.
120hz is only needed for gaming right? If so, that wouldn't be a consideration for me.
My seating position isn't right against the back wall, so I don't think rear speakers would be an issue.
I don't really understand what you mean by 'heights'? Sorry if I'm being thick.
To summarise what I understand from your reply, I could get monitor audio rears and centre that match what I have. Add an AVR and I'm good to go. Is that right, or do I need an RSW-12 sub-woofer too?
One supplementary question, do AVRs tend to provide poorer amplification than stereo amplifiers due to the cost of all the components for the extra channels?
Try both, you might find the AVR just as capable or maybe even better, but if it is worse or you just prefer how the A90 sounds/ergonomics you can use the A90 to power your fronts. Indeed on the gaming.
There are rears and rear surrounds. Using both would make a 7.1.4 system. These are at ear level, 2 to the side of the seating position fairly wide and 2 behind, but just 2 here is fine if you don't have the space or want the speakers around.
Atmos is an extension of the usual 5 and 7.1 to include a pair or 2 sets of speakers at ceiling level. This is the .4, or .2/6 if you have 2 or 6. The RS6 goes fairly low, no real need for a sub, I found music sound pretty good without. Might be nice to have depending on volume levels and film playing regularity,
Previous generations that was generally true, but they seem better now days.