Ryanosaur that makes a whole lot of sense. The AVR will have to be replaced as its not Atmos, but thats OK. If I get top back, do they replace my existing back floor speakers or are they in addition to?
No. If you added top rears they would not replace the bed layer surrounds. Also, if only installing 2 height/top speakers, you’d place them in the ceiling and just in front of the couch. However, if you’re adding 4 overhead, they’d be spaced farther apart. 45° fore and aft of the LP which you should be able to get close to.
I see you’re in Europe somewhere so look at XTZ subs. If you want to upgrade your sound, that is the first place to start. The problem with subwoofers is you can NOT put them into cubbies and expect great results. They really need to be out in the room. You can put speakers in compromised locations and still be kind of ok, but they deal with sound waves more directly to the ear(think line of sight, also, do not read as you can just go willy nilly) where subwoofers are basically all transmitted by the room. The room is beautiful, and you’ve made accommodations for the mains that you are happy with. Ok, that’s fine but if you are serious about upping your game, get a pair of nice XTZ subs. Try to have an open mind with regards to placement and putting them where they can work with the room. Every room is different, and require different techniques. Ryan and I have rooms that couldn’t be more different, and we’ve had to use different ways to get the best bass in our rooms. Still, I have no doubt if we visited each other’s space we’d find a great experience in each.
If you’re not willing to move the subs out of the cubby, then I wouldn’t bother with new ones, as they’re most likely in the worst possible place they can be, and also too small. But know that’s a conscious decision and if you can allow some latitude on subs and their placements you will be rewarded highly with bass that has power and depth. It will also make your other speakers sound better as well.
IMO, you would do well with a 5.1.4 system with dual subs.