Yeah man qwix is awsome no mucking around and fast.
I'd clear the cache and see how that go's but i dont think it'd do much in your case. dvd2xbox is what you should be using to back up your game, in any case the method you have been using seems to indicate to me that there are too many steps to backup the game and that could be the problem. Try and use the disc's in someone elses xbox to elliminate the disc's.
Since you are playing from the dvd-rom then maby the rom is on it's way out, thats harder to test for and is unlucky (in my opinion) but keep an eye on it in the future. (as the dirty disc error)
As for the dashboard Evox is fine I have changed the settings in the list to IGR no and TSR to disabled
and have no problems for the last 3yrs or so.