"Juggling" can be used generally in this sense to mean organising a lot of complex things at once. Women these days have to juggle the competing demands of a career and a family.
In this sense, it would mean that there is a special program to integrate the systems: apportion memory and CPU time between them, allocate time to end users, do backups, and the rest.
In this case, "systems juggling" is a compound noun.It is not the possessive "system's juggling". It is only this latter which would be exchangeable for the "juggling of the systems", even though it would mean almost the same thing in this case.