The same issue occured with a static IP address with the DNS-323 and the router, so I haven't tried with the Xbox.
As for the media, mainly music, however there are pictures and some videos as well. 99% of the music is DRM (aka the devil) free, whereas most of the videos are locked down with it.
Right now the solution I'm looking at is to get rid of that router and get something else, along with using a wired connection on the Xbox.
I have some CAT6 cables on order (my cables are CAT5 with one or two being CAT5e or whatever that enhanced version was), which shouldn't make any difference at all (unless I upgrade to a gigabit router).