CBass, thanks for the photo. Your geometry seems very similar to mine. Now that you've cut the holes, you are definitely into 7.2.4, or at least the speakers.

How far forward will you be sitting ahead of the rear Atmos speakers? I suspect the addition or loss either rear effects speakers will be a small impact in your room (like mine).
I know you are on a roll, but you may want to get everything else wired, purchased, and installed before buying the secondary amp. (Including furniture.) As you are going in-wall /ceiling for all but the Fronts, any of those can be driven by a decent 50 Watts per channel amp. If you have an old Amp/Receiver, you may want to try that as a test before going down a separate Amp road. That's my plan anyway.
Your Front Speakers should be the main focus now IMHO. I looked at SVS Prime and they are impressive based on the Reviews. The best deal I found on them in Canada was at
Electronics For Less but the center is almost $1,000 and the L&R bookshelf speakers are $700 each. SVS has few distributors in Canada (none here out west) and restricts their special promotions to USA customers only. If you could accomodate 3 Ultra bookshelf for the Fronts, you'd save $$ and it would sound better too. Of course their towers would give the best sound (although not by much according to other forum members who went from the bookshelf Ultras to them). They are $2800 for the pair.
I've decided on three of the
HSU CCB-8s as the reviews are off the chart, you can rotate the center speaker with no ill effect (so it fits on my entertainment unit below the TV without having to jack the TV up too high) and the cost is about $1500 CAD ($1154 USD) sent to Point Roberts nearby where my mother lives.
They did quote me to ship to Canada (in USD) below.
Product Name Qty
---------------------------------------------------
3.0 CCB-8 Speaker Pkg SB 1 $1039.00
Subtotal 1039.00
Shipping 215.88
Taxes & Duties 252.15
Total $1507.03
This works out to about $1960 CAD.
I haven't pulled the trigger on these yet as I need to see what the possible Duty & taxes are if I go pick them up from Point Roberts, Washington. (I need to visit Mom from time to time anyway & she lives in Tsawaswassen, BC =>5 minutes away from the border.) I've also been swamped with work, and other issues around the house to focus on the system for a while.
Hopefully my research can save you a few hours of effort.