I was looking at my system and realized I had not seen any type of mixer to configure my 5.1 speakers. I did fine a Realtek HD audio mixer in the Control Panel and started it. Prior to this, that icon had not been shown in the hidden icons section, just the Sonic stuff.
There are some settings which might be relevant. One is "mute rear output when front headset is plugged in". There may also be some volume level which is effecting the rear output. If it thinks it is a headset, it might be limiting the volume.
It doesn't appear you have done anything to damage your system unless the external speakers were faulty and caused some type of electrical short. If the speakers still work in another system and all your USB devices still work, it should be something simple.
I wasn't a fan of the way Windows handled sound prior to some of the recent updates. The fact the sound settings are not in the Settings section is just a nuisance.
Maximus Z790 Hero,
Intel i9-13900k
Intel BE200