btw I don't listen to mainstream bands who ridiculously polish their sound,I mostly listen to extreme metal bands,so you may know what kinda sound I'm searching for.
Thank you all for helping.
To be honest I'd get the HS3000 by Samsung. Little bluetooth receiver, so you can use whichever headphones you want with it (maybe different ones depending on whether you're at home/on the go/exercising or whatever), or even plug it into a stereo if you wanted via 3.5-3.5mm cable. It has Apt-X which is a must for listening to music via bluetooth for me, the Senn MM550X has Apt-X too but not sure whether you're referring to that one or the older MM550 set which doesn't sport Apt-X. Of course Apt-X support doesn't mean anything unless your source player also has Apt-X (as of right now not that many devices do, it'll work with non-Apt-X sources too though, but nice to get the future proofing). Can be purchased very cheaply too, which means you might be able to splash out on a better set of headphones and a headphone amp from within your $500 budget.
They will soon though, the iPad3 was the first, but you can basically put money on the next iPhone following suite. Given how cheap the HS3000 is might as well get the future-proofing into the bargain! For a non-Apt-X bluetooth headphone I would not pay anywhere near that money for the MM550. HS3000+~$300-350 set of headphones+headphone amp (or combo DAC/headphone amp) I think is a far, far better proposition. If you want just a regular bluetooth set of circumaural headphones pick up something like a Moto s805 or Sony DR-BT50, which can be had far more cheaply than the MM550.
IMO, IE80s outperform MM 550x, MM-550x cost that much because of higher production cost, especially for a aptx headset with good sound quality, but that doesn't mean the SQ is on same league as other similar priced-range IEMs.
I've listened to the new Harman Kardon BT headphones at the Apple store near me and they are pretty freaking nice for Bluetooth headphones. I'm gonna pick up a pair, they're only $250. I listen to primarily metal also and they handled the genre very well