OK i will try and help with what i know, first of all as your using a router DHCP is def the way to go, and should be relativly very easy for shoutcast to find a connection.
So first things first and check your XBMP System settings -- does this show the Network as DHCP if it does whats your IP showing as underneath, does this correspond to an IP your Router is free to send/receive on via DHCP settings.. (it should be) If so you should literally be able to go to shoutcast.com and save a .pls file to your PC (rename it so you know what it is) then upload to your Xbox and away you go..
heres my config for the IP stuff - The asterisks should make it DHCP, i use avalaunch as a dash which is also setup as DHCP.. and my Xbox plugs straight into the router.
My Router is actually 192.168.254.254
My PC is 192.168.254.2
My DHCP settings on my router are open to send recieve on 192.168.254.1 through to 192.168.254.19 so my Xbox should find any setting from 192.168.254.1 through to 19 except obviously 192.168.254.2 which is the PC
My XBMP config IP info..
<address*>192.168.0.3</address*>
<subnet*>255.255.255.0</subnet*>
<gateway*>192.168.1.1</gateway*>
<nameserver>192.168.254.1</nameserver>
<playlists>$HOMEplaylists</playlists>
<timeserver*>207.46.248.43</timeserver*>
Now this all works for me so hopefully may guide you, be aware that i did also have the same problems as you.. i.e Time Outs..
I think it was where my Evox disc which i used to setup the box was set to static and not DHCP !!!! It seemed to take over my network settings and was making XBMP (which i used as a dashboard at the time) think it was on a static network even though the XBMP config was setup to be DHCP !!!!, i found out a cure for this by chance and literally inserted a Evox boot disc in my box which was setup to boot as DHCP not static.. I then restarted my box and all of a sudden my shoutcast worked !!! Wether this was a fluke im not sure but i dont think it was...
I now use Avalaunch as a dashboard (also set as DHCP) this finds the downloadable skins/newsfeeds etc and was a good sign that XBMP shoutcast would work...
Hopefully their maybe some info in here which may help you, if not, sorry for the long useless post.. lol
Goodluck with your mission, believe once its working your`ll be chuffed to bits.. its a nice feature , i like the fact you can record the shoutcast music as mp3s.. think thats neat..