I've been snooping around and just had to post my 2cents for mysterious. lol. **** the 770's, bud. When you shop for electronics you gotta think "expandability". No point dishing out a lot of moolah on something outdated, that wont benefit you in the long run. I'd bite the bullet and go with the 990's, worst case scenerio is you HATE them and get a refund within the 2 week trial period. I personally own the 990 600 which are absolutely phenomenal, to say the least. I just bought the lyr for them today too :)
At the end of the day its your money, good luck and I hope you enjoy your new set of cans, whichever they may be.