It seems you have missed some steps...
NOW you can config SLPs...
These were my notes for 8.0 AIR config. There may be additional steps for security certificates.
Please read NBU docs.
Further to all the above, you will need to setup the trust relationships between the master servers (this is done when adding the trusted master server through the GUI as described by @Marianne ).
The second part is you will need to establish trust between the source storage server and the remote domain - this is decribed in the Dedup Guide in the section titled "About trusted master server for Auto Image Replication".
Once all the trusts are established, then the dialog box you were stuck on should provide the target MSDP pool to replicate to. You will need to supply the remote storage server's password at that stage (it will determine the username automatically).