I have auditioned the Q950s along with the R900. By reputation the Q750 is a good speaker. My experience with the other two is that they do sound good. That said, I am not a fan of KEF and would urge you to audition them before you buy them. My experience may be an outlier in the spectrum, but I found them fatiguing after about 30 mins. By the time I was done with the audition, I was done with KEF.
They are still a respected brand, and as I said: the speakers I auditioned performed well and are generally well regarded.
I would urge you to consider better subwoofage. That will be a week link in your system. I'm not suggesting you go out and blow 2K on an Uber-Sub, but shopping around may provide a better long term solution that you can grow with for several years while planning the next upgrade.
In fact, you already have the PB2000... you should keep that and plan on adding a second of those by next year. Matching Subs is a benefit when running multiples. The Cube in your list above will likely not perform on the same level as the SVS and will actually limit your usage of the SVS in the system.
Regarding the electronics, the Denon 3600 is a very well respected AVR and I would recommend that over the others. The inclusion of Audyssey XT32 makes it a pretty solid solution for room correction, especially with the Audyssey Editor App.
I've been eyeing the 3600 to replace an old Onkyo that blew just a few months ago. Usually they see a good price drop when the newer models hit (3700) but Covid is wreaking havoc with production and distribution, and I suspect that is why the 3600 hasn't seen the expected price drop.
Be patient and keep looking, learning about the gear in the meantime! You will save yourself a lot of heartache by not running out on an impulse spree!