After a couple of phone calls and a lot of experimenting, I found buried deep inside some developer docs a MIME extension that has to be registered in a web server in order for the 7100x to recognise an ADPCM ringtone.
Two conditions apply:
1. The ringtone file must have an extension .adp
2. The adp extension has to be registered in the web server as audio/adpcm - in IIS this is easy to do, just add it on the server options window.
Once I registered this extension, I was able to post some ringtone.adp in the server, and have the BB (7100v in my case) download it, i.e. http://www.my-server.com/ringtone.adp
I have titled the post half solved as I still don't know the correct ADPCM format the ringtone should have. FYI I've tried 11025 and 8000 Hz, 4-bit, but the BB doesn't play them, it just pops. The file seems to load and the player comes up though.
P.S. with the router problem, is it possible some posts and users have been lost? I've had to re-register on the forum, as it appears that my user account and my posts have gone.