Two (or less) easy steps:
1. If you have a firewall, open the necessary port(s).
2. If you have a router, configure it to forward the necessary port(s) to the DNAS machine.
Check out the Sticky post titled:
SHOUTcast: Important Info & Answers to FAQs. READ ME!
Scroll down a bit and look for the section titled:
DNAS Stuff -> Errors -> Fixing [yp_add] yp.shoutcast.com gave extended error (Cannot see your station/computer (IP: xxx.xxx.xxx.xxx:xxxx) from the Internet, disable NAT/firewall/ISP cache (Connection timed out)
Are the necessary ports open in your firewall and are they being forwarded to the DNAS machine?
Check out http://www.radiotoolbox.com/cantheygetin
and see if the reported information there helps.