Just to say I think I understood what you were doing from the start!
Ok so you can connect an HTTP download from the server, but the upload is proving to be an issue.
Now I know that when I connect to upload to an FTP site sometimes I have to download/upload in Passive mode because of the firewall, I can't just upload as normal.
I wonder if there is some nasty rule in your firewall that is stopping you from casting?
If you email me the ip/port/pass for your SHOUTcast server (on your linux machine) then I can try to connect to it myself to see if it's a configuration issue at your server, or an issue at your broadcast machine.
I don't know where you are casting from, if it is somewhere you can
talk to the network administrator, and ask if he can monitor what is getting allowed and dropped to your box when you try and stream then you may be able to identify what is stopping it. (Your company/uni firewall may block large uploads to save it's bandwidth for example, ours does
I had to sit with our sysadmin and watch my machines traffic to identify how to blast the holes for SAM, then I found out SAM was a pile of shite anyway...