I am by no means an expert, but just finished putting together my home theater system. What a chore that was, leading to crown molding to hide wires and all the fun that goes with that. My situation was/is much like yours. I have an "L" shaped listening/viewing area, started with the receiver I wanted, and then picking out the speakers that would fit in my budget, with the exception being my choice of speakers was also dependent on the size, due to placement space and my listening viewing space being over 2 times yours. My home theater is set up in the upper left corner of the "L" area(living room). One surround in the lower left corner(dining area) and the right surround middle ways on the lower right wall(kitchen). The surround speakers are as close to equidistant from my main viewing area, which is my couch, set up diagonally, directly in front of tv/home theater setup. I started with the Yamaha HTR-4066 and added JBL ES20 speakers for my left and right fronts, JBL ES25C center speaker, JBL ES10 for surrounds, and Yamaha YST-SW216 subwoofer. Again, I want to stress the size and cost of the speakers were the determining factor in the purchase of these JBL's. Had I more space I would have went with the JBL ES30 for left/right fronts and JBL ES20 as my surrounds for maybe $30 or $40 bucks more. The point I want to get to though is, I am blown away by how good what I went with sounds. No need for the bigger speakers for what I was looking to achieve. I couldn't imagine how much better it would sound in a smaller area, such as yours. Anyway for what I have in the whole system, I couldn't be happier with the sound this setup produces for my needs. I shopped online to find the best deals and availability, but have right at $550 in speakers.
JBL ES25C-$160.45
JBL ES20-$138.44/pair
JBL ES10-$149.75/pair
Yamaha YST-SW216-$104.99
In your case, with more allowance for speaker size, I might go with the ES30's as fronts and ES20's for surrounds, for as little as $40 dollars more, putting you at your $600 budget.
Hope this helped. Let us know how it turns out.