To access the latest versions of Rocket Player or iSyncr, ou can sign up to be a beta tester in the Google Play Store (either Rocket Player or iSyncr). Once you've successfully joined the beta, an update for the app will be available on Google Play.

Rocket Player Beta Sign Up
iSyncr Beta Sign Up

Click Become a Tester.

Wait for up to 24 hours, then look for an update to Rocket Player or iSyncr on Google Play.