I'm not a pro here and I do not have personal experience with the SVS Prime satellites or the Bose 321, but I'll comment in case it's helpful. I think
@Pogre has quite a bit of experience with SVS speakers so he may be able to provide better insight.
I have three Denon AVRs and I have not had any reliability problems with them. In my experience, Denons throw a lot of heat though, so I'd make sure they yours has room for air circulation (I suspect that a lot of reliability issues with AVRs in general are related to overheating, but that's a topic for another day and thread)(I know you didn't ask, but take care putting a Blu Ray player above a Denon so as not to cook it)
The SVS Primes seem like decent speakers so I don't think you'll be disappointed. Having said that, you might be able to do a little better by adjusting your spending.
First, do you need 8k capability in the AVR? If not, you might be able to save a few bucks with a refurbished 4K receiver such as the S950H:
https://www.accessories4less.com/make-a-store/item/denavrs950h/denon-avr-s950h-7.2-ch-x-90-watts-a/v-receiver-w/heos/1.html
I have not bought anything from accessories4less but quite a few people here seem to have had good luck with them.
The SVS Ultra bookshelves get great reviews:
Review: The SVS Ultra is a two-way ported bookshelf loudspeaker designed with impeccable build quality and aesthetics and grounded science. Do they live up to the SVS name? Read on to find out.
www.audioholics.com
The Primes also get good reviews, so they're not cr*p by any means:
Looking for a pair of bookshelf speakers in the $500 price range? We have compiled a list of our top choices for bookshelf speakers at that price point for 2021.
www.audioholics.com
I bought a pair of the Ultra bookshelf speakers (piano black) from the SVS outlet a couple years ago for $299.99 each. The description said they had blemishes in the finish, but I was barely able to find the blemishes. The problem, of course, is that even at $299.99 each you wouldn't have any budget left for surrounds or a sub, unless you get a lower priced AVR. Assuming your budget can't be stretched, the outlet Ultra bookshelves would probably not be a good option unless you wanted to buy a sub and possibly surrounds later.
Some people would say mixing speaker brands is like breeding cats with dogs, but, at $350 per pair (and a little assembly time) the Philharmonic Affordable Accuracy Monitors would probably make decent surrounds to go with Ultra bookshelf speakers:
I have not heard the Affordable Accuracy Monitors, but they appear to be quite neutral so I'd think they'd pair reasonably well with Ultra bookshelf speakers (mixing speaker brands is a never ending point of contention, so my post will likely trigger someone to post that speaker brands should never be mixed due to "voicing" concerns)(I tend to think it depends on the specific speakers in question, but that's just my opinion).