Don’t assume that putting your display on the long wall is necessarily bad. It will give you the option of having a wider front soundstage w/o getting to close to the side walls.
What Axiom speakers does your relative own? I ask because I would personally change your speaker selection unless you have already heard all those speakers and know already that you like them.
I would consider changing your VP150 for a VP100 and using the money saved toward upgrading the QS4s to QS8s especially if you plan to run 5.1 even if just initially. I do think the VP150 would work fine in your setup I used mine in a similar situation with my M22s and it blended perfectly. But from what I’ve read the QS8s are noticeably better than the QS4s and I don’t think changing from the VP150 to the VP100 would be as noticeable.
Another suggestion since your seating is so wide compared to your display is to not even use a horizontal center speaker. With wide seating the better horizontal dispersion of a vertical speaker like the M22 or M2 would almost certainly perform noticeably better than a horizontal speaker. The same would go if choosing one of these speakers to put the savings toward upgrading to a pair of QS8s.
As for rear speakers I’m not sure you would get a benefit worth the cost of another set of QS speakers. As you intend I would start with 5.1 and try playing with the surround speaker positioning. You could even put the surround speakers in the back corners like one is pictured. This could help create a better “phantom” rear image. You could eventually order a pair of rear speakers and try them out. If it turns out not to be worth the upgrade return them within 30 days and I think for most of the small speakers like surround and bookshelf it would only cost $30USD a pair to send back.
Cheers,
Dean
