Tips for a budget home theater system

I'm moving into an apartment with my fiance in about a month - it'll be the first time either of us will be living without roommates, so I wanted to splurge a little and get myself a receiver and some speakers (I'm thinking 5.1) for the living room that I can really enjoy. I've had a pair of M-Audio AV40s since 2011, and they sound alright, but I'm hoping I can do a lot better.

I'd like to spend about $600-700 total (closer to $600) and I know that's pretty tight. I've been doing a bunch of research over the past couple weeks: For receivers, the Denon AVRS530BT seems to stand out for the price, but I'm not attached - that leaves somewhere around $400 for speakers and a sub. https://trackeasy.fun/usps/ https://showbox.tools/


The room they're going into is something like 15x15, though I don't have the exact size. Any tips, suggestions, or experiences that you'd be willing to share?