Still trying to understand oss sound in Haiku

I posted here a day or two ago about an issue I had with not being able to run the osstest in Haiku r 40448.
Indeed, I have posted quite often about sound problems with oss in Haiku such as this, this and here's another one.
However, in looking back over an old thread that I initiated in the oss-4front forum, I spotted something that hadn't registered with me before.
In the seventh post in this thread, it is stated that

now, the media addon should not be able to output sound when osstest/ossplay is using the card actually if he can use osstest/play they the media addon likely didn't open it correctly or it opened another channel but it should take them all might want to try killing media_server and media_addon_server and restarting it from Terminal

This seems to imply that if media_server and media_addon_server are in use, then osstest cannot be used successfully and, vice-versa.
Obviously, to play media you need the media servers, and in this case osstest won't work.
So, I killed both media_server and media_addon_server and then tried osstest again, and now it played perfectly.
However, to get media playing again, it wasn't enough just to restart the media_server (/system/servers/media_server &), but I had to reboot.
Looks like there's still a lot to learn here.