For anybody who might read this in the future:
When enabling ecomanager and the new version of the SSB simultaneously, the SSB score board takes precedence and hence the broken score board of ecomanager get's overwritten.
Regarding the "selection sound" issue of the ecomanger that I described above, the solution is to explicitly enable the "common mod tools" mod as a UI mod. Just having it installed is enough to have the mod's functionality work, but to fix the sound issue, you need to enable it as well.