[icecast] streaming through a firewall

[ianux]

I'm running the latest versions of icecast and ices on my linux
box behind a NATed network routed by another linux box with iptables.
The stream is available on the local network (i.e http://192.168.0.20:8000/example.ogg)
tested with winamp 5.
but the stream is not available on the net (i.e with the public IP)
I haved forwarded port 8000 on the router with the same lines I did for
eMule, FTP, Bittorrent, ssh, and all that work fine :
iptables -t nat -A PREROUTING -p tcp -i eth0 -d 82.66.x.x --dport 8000
-j DNAT --to 192.168.0.20
iptables -A FORWARD -p tcp -i eth0 -d 192.168.0.20 --dport 8000 -j ACCEPT
what can I do more to make it work ?
is it a problem of icecast or ices config ?

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