Reach Module is a single-band, while Reach RS2 is a multi-band. It means that Reach RS2 won’t operate as a rover if Reach Module acts as a base. A multi-band receiver requires more satellite signals to calculate its position precisely. You can check more information in this thread.
In the last paragraph my colleague Svetlana tells about a similar case when Reach RS+ is a base. Don’t be misled by that: Reach RS+ is a single-band as well as Reach Module.
What do you mean by using directly? If you work in RTK, you can collect points and export them in different formats: CSV, DXF, SHP. It doesn’t require any post-processing procedure.