I never used DP Express, only the Enterprise Version but from what I read so far it is basically the same Product and also uses a Server that acts as Catalog Repository.
That Server should also be the one where you create the SRD-Disk or where you get the SRD-Files from.
That one has to be active and reachable for a DR-Restore work, a client never directly contacts a MediaServer unless instructed from the CellServer to do so.