Nicola,
If I understand you correctly, you have two RemoteRig servers,
but can only access one over the DynDNS address.
I would assume you know that you must assign two different SIP
ports, otherwise it won't work. In this case, you must forward
the second port in your router.
For example, the first box may be just iz7anl.dyndns.org, but
the second one would be iz7anl.dyndns.org:5601.
The micro client has the port number below the IP address,
so that is where the 5601 in this example would appear.
73,
Mitch DJ0QN / K7DX