The StarTeam Server to which you connect must be MPX-enabled. However, the StarTeam Cross-Platform Client does not have to enable ActiveMQ MPX to take advantage of MPX Cache Agent. ActiveMQ MPX provides properties about files and other items. MPX Cache Agent provides file and/or object caching. Using both would be typical but is not mandatory.
MPX Cache Agent use can be enabled either through personal options or in server properties, specific to the server you are editing. Personal options would only be referenced if no specific settings on the server have been made.