That dent won't affect the sound at all, just a dust cover. There are a couple of methods you can try..I've had good luck using a vacuum cleaner attachment on a lower suction setting. Just move slowly towards the dent and often it will pop right back. Or, Axiom has a video using masking tape. I've even used a small strip of duct tape to do the same..

http://www.youtube.com/watch?v=xFbvhokVrPI


M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB SonyUBPX800