Hi,
6.7.1 is the current version of SonarQube as well as the current LTS. You are more than 2 LTSs behind, and you're going to have a hard time finding support for your current version. I urge you to upgrade at your earliest convenience.
That said, this is more a question of your SonarJava version than of your SonarQube version, since each language analyzer handles its own language-specific coverage reports. However, once you get to SonarQube 6.7.1 (and a current version of SonarJava), you'll find that you can specify multiple report paths with the `sonar.junit.reportPaths` property, so the question of finding a compatible merged format goes away.
Ann