Thank you so much for pointing me to the right place.

Your query change didn't quite help me, it basicly retreived all my users as admins.
So this is what I came up with:
Change this, (*joomla_install*/components/com_fireboard/template/default/plugin/report/report.php row 97):
[code:1]
SELECT id FROM #__users WHERE gid >= 24
[/code:1]
... to this:
[code:1]
SELECT id FROM #__users WHERE (gid = 24 OR gid = 25) AND sendEmail = 1
[/code:1]
This sends reports only to admins & super admins with enabled "Receive System E-mails".