Test Cases which involve multiple software projects

We have what we believe o be a very common situation:

• a server which provides various REST APIs
• various client apps (iOS, Android, Web, Desktop) which communicate with the server
• the server and the four client apps are technically 5 different software projects with their own releases and builds
• we use test automation
• most of our Test Cases involve at least two of the above software projects (server + one of the apps), e.g. the login tests, where the apps are expected to check the credentials against the server
• some Test Cases involve three or more of the above software projects, e.g. the iOS app sending a broadcast which should be received by the three other apps
• we want to test all kinds of compatibility scenarios like "can iOS app v18.3 login against a server v19.1?", "can Android app 18.3 receive a broadcast sent from iOS app 19.2?"

How would you do the above in SpiraTest? We're quite excited about the Test Configuration feature, where we could Test Case parameters like "Client1, Client2, Server" and create custom lists with all the currently supported app and server versions, but then we miss out on the traceability via Release and Build.

Alternatively, we could account for the fact that each of our 5 software projects above has their own releases and builds by creating 5 corresponding SpiraTest projects. However, how would we deal with Test Cases which involve multiple software projects (see above)? We could use the cross-project feature introduced in SpiraTest 5.1 by expressing our expectations for such multi-project scenarios as SpiraTest Requirements, copy the same Test Case into all SpiraTest Projects representing the involved software projects, and link all those Test Cases to the one Requirement. However, how would execute all those Test Cases? Using Automation, we're scheduling Test Sets and have RemoteLaunch execute them. How would that work if we're running a test which involves multiple software projects, represented by multiple Test Case clones across corresponding SpiraTest projects?

Any suggestions very welcome!