domain mapping and plesk

Hi, I've try to find an answer to my Q on forum without any luck..
I've install the plugin and copy the sunrise.php to the right location, activated the plugin, add my IP address to the plugin settings, added a test domain I own to one of the site on the network (sub directory, Not sub domain BTW) - All looks good so far. My server has plesk install on it.
After adding an A record for my test domain on GoDaddy ( all I can see after going to my domain is a plesk welcome page which shows automatically after I add an A record to a domain with my server/plesk IP.
I guess my IP's are automatically goes to my plesk and not to the main domain (the multisite domain) that install under plesk.
I'm not sure I understand how to make it work..? Am I missing something?
Please help.

PS, If it can make things easier, I have another domain Ill be happy to use as an NS domain, I mean that my clients will be able to add 2 name servers ( and to their domain ( for example) and it will connect it to the right domain with the right sub directory of the user website. But I have no idea how to setup the records for the domain. Is it possible?