problems with re-mapping and re-directing

Hi,
I have a multisite installation @clixbits.com that is all working fine, including the re-mapping plugin.

The problem comes when I try to re-direct some of the domain names.

an example.
I have setup sydneycarmarket.com.au as a site.
I also own sydneycarmarket.com and want to re-direct this to the sydneycarmarket.com.au address.

I have tried ‘parking’ the .com name and then applying a re-direct which is simply re-directing to the front page of the root site clixbits.com where I have the wordpress multisite installation.

The other option I have tried is setting up addon domains, and then using the htaccess in those domain folders re-directing to the relevant .com.au site. which works in terms of re-direction, however when I log in as the ‘super admin’ and click to go to one of the dashboards of the sites that now have an ‘addon’ redirect I can’t access the dashboard of that site. I have also tried accessing the dashboard directly by going to sydneycarmarkets.com.au/wp-admin and I get the following error:

“Not Found
The requested URL /wp-admin/ was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. “

Does anyone have any ideas on how I can achieve my goals?
thanks in advance for any help.