Could it be something along the lines of this bug report?
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Binary package hint: mediatomb
Currently mediatomb is putting invalid routes in /etc/default/mediatomb. The routes do not need to be there at all and should be removed. The lines I am speaking about are:
/etc/default/mediatomb
ROUTE_ADD="/sbin/route add -net 239.0.0.0 netmask 255.0.0.0"
ROUTE_DEL="/sbin/route del -net 239.0.0.0 netmask 255.0.0.0"
These should be changed to
ROUTE_ADD=""
ROUTE_DEL=""
Since most networks are not 239.* this is definetly not valid.
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This is the multicast line of the mediatomb startup script from what I gather; you could try changing the routes. Also I thought this might be helpful information for the developers so that they know what mediatomb is trying to do and why it might be conflicting.
Let me know because I am VERY interested in making this happen on my own network. For pretty the same reasons (ps3, xbmc etc.) and I have a couple shiny new 1tb sata2 drives to throw everything on as well...