I don't understand a lot of what you are wanting, but I do know you can host the main domain on one server, and a sub-domain on a different server. Perhaps you can build the new site on the sub domain/new server, and when all is complete, move the domain name to the new server or have the host put an auto re-direct on the original server site to the sub-domain.
You change the A name for the sub to point to the original DNS. There is an article that describes the steps:
http://css-tricks.com/put-a-subdomai...ferent-server/