Messages between the Silent-Vault wallet client and the SVX exchange are implemented as private extensions to the XMPP protocol. These messages pass through a gateway server, which itself communicates with the SVX using extended messages. The specification of how both the c2s and s2s messaging is defined can be found in the Xmpp-extensions.zip download, which is obtainable from the Documentation file gallery. (See the "Files" link in the top menu above.)
Note that the messaging related to the SSM (Silent Silver Marketplace) is not yet supported in the client, nor is the server side deployed. It is included simply to serve as an example of how an adjunct marketplace might be implemented within the client itself, without any need for web browser interaction.
The XMPP extensions defined by Voucher-Safe to perform wallet operations, payments, etc., can be obtained from the Voucher-Safe dev site. (Note that you will need to register a login there in order to access the file galleries.)