I do not know if you already tried, pavucontrol? If not:
In a terminal: sudo eopkg install pavucontrol
And to run it in a terminal type: pavucontrol
(it is also under sound & video "start" menu, pulse audio something)
Maybe look specially under the configuration tab, there the different profiles, but the other tabs too
Sound via the monitor you are trying, maybe the output from Solus is just too loud? And of course there is the monitor audio level then too...