Whenever you sell something new, its always a loss. You might have to drop the price more to attract someone and sell it faster, but with some patience you could sell it for 20 less. Of course there are lots of angles to consider for its value. Do you still have the box and all the accessories intact and immaculate? If you can package it like new, boast it in your ad. Try finding free online classified ads, like kijiji (works in Canada, not sure about other countries).
As for Phenom and Nvidia, they work just fine, but if you go SLI, now that's fine too but the quality AMD SLI mobos are very hard to find. I use the M4N82 with a AM3 Phenom 2, no problems at all so far.