I'll try best explain the setup/senario:
You're company is merging (buying out) with another company. The other company is very small (a single site that will be connected by fiber) and has one (L2) network which runs on a non-Cisco switch and they have a Cisco ASA and DSL.
You are going to be placing a new Cisco (of course) 2821 router at the remote site for connectivity along with a good L2 (3560) switch for your network connectivity. The company your buying out has several site-to-site VPN connections for access to several servers.
You want to keep in-place for now their site-to-site VPNs, but still let those servers have access to you're companies internal network.
You're plan is to have you're companies new switch at the off-site hang off one of the ethernet ports, and the company you're buyinh out connect to the other ethernet port. You want to route traffic between the two networks (provide some security where needed) while allowing the site-to-site VPN's from the company your buying out to still be functional over their ASA, and not you're companies ASA.
The routing seems to be a bit strange on how to make this work. Any suggestions would be gladly appreciated.