Bookshelf speakers for $500ish

Either the Rega RS-1 or the Silverline Minuet Supreme Plus will work extremely well on your small room as they are not fuzzy about placement.

Supreme Plus having an advantage on Jazz over the RS-1.

RS-1 having an advantage over the Supreme Plus on Classic/ Small Chamber.

No idea if these are any good, I happened to see the review right before I saw your thread. They are active, maybe you'd like to get rid of that Marantz

http://noaudiophile.com/JBL_LSR305/

One of my favorite "bookshelf" speakers over the
years was the Sequerra Pyramid MET-7. They do't go very deep,
but their mid-range and treble are excellent. I used a small
subwoofer with the pair I owned, but without a X-over it's
hard to get a good blend. The speaker has been in production
for 30+ years, and while a new pair is well above your budget,
used examples can be an excellent buy (I recently saw a used
pair for $600), and there is a pair currently for sale on Ebay
for $375.
Check out the Internet for various reviews.

Here's an interesting listing for a pair of Rega RS-1s. No affiliation with seller.

Check out the Vanatoo Transparent Ones if you don't mind buying active. Tons of rave reviews! They start at $499.00 in black with multiple options including Bluetooth and Airplay.

From the Vanatoo website:
"Check out our home stereo speakers in the comfort of your own home with the Vanatoo 30 day audition period. If you decide within 30 days of receiving your Vanatoo speakers that you are not totally satisfied, you can return them for a complete refund. All we ask is that you pay for the return shipping".

Michael Fremer bought the review sample :-)