I'm currently running a pair of Athena AS-B2.2s through my Nuforce Icon as my desktop audio setup. Looking for a worthy upgrade, preferably < $300. Currently there are a pair of Monitor Audio BR2s on Audiogon for $250. Is this a good deal, or could I offer lower? I'm also open to other recommendations. 6"+ woofers not mandatory, but I don't have a subwoofer so I like the extended low end response range.
Upgrade for under $300? That's a tough one. There are some options if you can swing $1000, maybe a little over. You don't have to buy it all at once either. Denon makes what I call a mini receiver plus for $600 without speakers, $800 with speakers. It has a built-in cd player and iPod dock, 2 analog inputs, 1 optic digital, ethernet and usb. You may want to check that out and save up.
I think the OP is looking for speakers James, not an overall upgrade. Cryptic, check out the thread in the Speaker section titled Speaker Bargains!. Lots of suggestions in the price range you're looking at. If you have questions on a specific speaker come back and ask it.
The Athenas during their time were considered bargoon giant killers by some. An upgrade for less than 300 is unlikely. The only suggestion I have is maybe some Paradigm Atom v5/v6. These a nice, cheap speakers.