Hi Matt. Welcome to the forum!
For the money, I believe the following will give you performance that's very tough to beat:
- Sub $270 See this post:
- AVR $220 Factory refurbished Denon AVR-X1000:
The Denon AVR-X1000 does not have HDMI 2.0 or 4K/Ultra HD compatibility, but has the potential for superior sound quality by virtue of running the very good Audyssey MultEQ XT.
For HDMI 2.0 and 4K/Ultra HD compatibility at that price, you would need to go for something like the($190+shipping), but you give up ground on sound quality due to the lack of Audyssey. (And possibly not all that future-proof anyway.)
Edit: In respect of future-proofing, have a read of this article:
The Denon AVR-S500BT does not indicate HDCP 2.2 compatibility for it's HDMI 2.0 port(s), so when native 4K content eventually arrives, it will not accept it. Therefore, scratch the S500BT from consideration.