These are the people who made your Jukebox, Speakercraft simply rebadged it!
[Link: imerge.co.uk]
I don't see why you would need the RSA 1, that is simply an interface for the MZC, which you don't have.
Contact Imerge direct, unless you can find what you're looking for on their site.
Regards Mark

This is from the 'Dealer' section of the Imerge website:

RTI have created a simple yet powerful two-way module for controlling Imerge media servers. Incorporating the XiVALink3 protocol, this new module is compatible with the MS5000, MS1 and S3000 (upgraded to 3.6 or higher) and offers the following functionality:-

Features:
■Audio & Video Library
■Browsing by artwork, tracks, album, artist, genre, year, era & playlists
■Full metadata and artwork over TCP/IP
■Build Play Queues (Jukebox)
■Film Synopsis
■Transport control
Version: 1.0

Notes: This driver is for Imerge and other XiVA-powered Media Server systems. The driver should be used with an IP connection but can support an RS-232 connection.

You can obtain this from RTI.