To setup SBS for multiple domains go here:
1. Add the group using the SBS Group wizard (be thought full with this name as it will be used as the email name when the email is sent)
2. Open the Exchange Console from the start menu
3. Click Recipient Configuration and double click to edit your newly created group.
4. Click Email addresses and add the email address for the new domain. Remove the check mark for automatically update policy. And click "Set as Reply"
5. You need to now grant "send-as" rights to the end user(s). Right click the "exchange management shell" from the start menu and select runas administrator.
6. run the following command with your sepecific options:
Add-ADPermission "YourGroupHere" -User "EndUserHere" -ExtendedRights send-as
That was it!
Now - be sure your secondary domain is setup and working before attempting these steps.
