I'm suffering from a short attention span right now.
If you Mirror a domain you've set up here, it'll work at CLIENTDOMAIN1.dreamhosters.com or SUBCLIENTDOMAIN1.dreamhosters.com
Unless something in your domains have the real domain name hard-coded and makes a call to your old site(s).
The long term fix is to edit your DNS here for xxxxx.net (I presume in your example that xxxxxxx.net is the same YOURDOMAIN.net for all of them). You'll need to add custom DNS records for YOURDOMAIN.net so that ns1 and ns2 point to ns1.dreamhost.com and ns2.dreamhost.com. You'll need the IP addresses for the dreamhost Name Servers to verify the change.
You'll have to go to your domain registrar to update the Name Servers for your domain so they point to the new DreamHost IP Name Server addresses.
The transfer of activity from your old site to the new site will be uneven as it takes a while for DNS to catch up for people around the world.