Go for the X. I have one X12 on an saz-1500 and it's louder, hits the lows better and cleaner than my old RE SX 15 did. Cant wait to finish my electrical and get both of them hooked up!
I did not enjoy the multiplayer at all. The weapons are horribly unbalanced, the spawn system promotes spawn killing, the online play needs some serious work.
I can honestly say ive only had one problem with the campaign so far. The orders are not clear enough. I havent run into any game breaking bugs like you however. Strange..