I don't think you can touch the MMG in that price range, but there is a very big caveat; Maggies take a lot of power to drive, and you don't have enough power. That makes them cheap to buy, but fairly expensive to enjoy.
I am not sure that your reciever is rated for a 4 ohm load to begin with, so I am wondering if there is a possiblity that you could not only be underdriving the speaker, but potentially doing a bit of harm to the speakers and reciever.
I would suggest getting a seperate amp and using the Onkyo as a preamp. Maybe an NAD 218thx? If you can find one, it's a v good, inexpensive amp with tons of headroom.
As far as other speakers in that price range, I don't think there are many if any in the same league, but I would look at some excellent Paradigms or a smaller Definitive Technology (BP 7006), those can sound great. The Def Tech has built in subs, tons of slam, and still excellent resolution, very good speakers.
Good luck.