Need help setting up a service definition for znc

Hey guys,

i could need some help setting up a service definition for znc (an IRC
bouncer). 
The behaviour of znc is that it spawns a server on port 31337/tcp and
connects as a client to several IRC networks. The networks i have
configured in my installation are using the ports 6667/tcp, 6660/tcp
and 9999/tcp. 
The problem i have is: The server runs fine, but it has some problems
with connecting to the networks. It is definitely a firehol/general
firewall problem, because everything works as expected when i disable
firehol completely. 
My current service definition for znc looks like this:

server_znc_ports="tcp/31337"
client_znc_ports="default"

The funny thing is: When i change something in the client ports config,
and apply the new configuration, znc manages to connect to the networks
for some time, but will soon disconnect with a "No route to host"
error. 

I assume there is some kind of port shifting happening, so i tried to
include the kernel modules which are also part of the IRC service
definition. The result: znc was no more reachable at all, even the
server side was not reachable.

So i have no idea how to resolve this issue, and therefore i am asking
here, hoping that someone of you has already created a working config,
or has some other idea how to check what's going on here.

Thank you very much.

Yours, Simon