Justin
I've described these problems before. I thought they might have been fixed by these major upgrades.
Plasma has no audio, ever. I've tried with the music manager (Ellsa?) and with VMC. No system sounds, either.
Mate's monitor problems are harder to describe. Both monitors display the background during login, but after my password is accepted the right-hand monitor (VGA) goes black. The left-hand monitor (HDMI) works normally, thus I was able to start a terminal to do the upgrades.
When I started the displays setting dialog to verify the settings, and clicked [Apply], both screens turned black. The right-hand screen was pure black, while the left-hand monitor had a row of garbage at the top, and otherwise black. I could only exit by a hard shut-down.
Thankfully, the Budgie installation works perfectly, and always has, so I'm pretty sure my hardware is fine.