A few things jump out, first, this isn't about your speakers, which according to their product description, are standard 1/8" audio jack driven, and USB powered, not usb audio.
So the actual question is why isn't your audio software directing output to the specified audio port.
If you use pulse audio control, that has a convenient way to check the output device actually assigned. Note that you have to generally disable other devices to get pulseaudio to consistently direct the output to where you want it to go, at least I always do. You also have to select the right profile for that hardware device, in this case, it's probably 'analog stereo output'.
So the audio out port you are using has to be from either your nvidia or intel audio device, and pulseaudio has to be told to use that one, it rarely in my experience actually picks the one you want without any manual intervention.
Again, you may be confusing yourself by mixing up where that output is going and the speakers, the speakers you can largely ignore in this, since they are just passive recipients of an audio port signal, and the problem here is probably where that signal is actually going internally for pulseaudio.
The Jack integration may or may not interfere with this, but my guess is if you check the pulse audio volume control thing, make sure the configuration tab shows all audio devices disabled that you aren't using, that is, all off except the one you are using, then the 'output devices' tab port is set to the correct output port, which for a 1/8th inch audio output is going to probably be headphones, it depends.
Again, Jack audio may alter some of these factors, but this would be the first thing I'd check. Almost always when I do not get audio from an output port, aka, plug, it's because these two things were not configured/set correctly, and almost always, pulseaudio fails to automatically detect in particular headphone port changes, maybe also pre out, line out ports. Which port to use depends of course on if you are sending the speakers a line signal, which you would have been sending to your receiver, or a headphone signal, which means your local software volume is controlling the levels, not the volume control on the speakers, if they have any. It sounds like your speakers get a line level signal, and you use the speaker volume controls to adjust the levels.
Bluetooth may also still be grabbing the signal, bluetooth audio is not awesome in linux, and it may just not be releasing the audio, I don't know how that looks because I don't use bluetooth audio in linux since bluetooth is inherently lower fidelity than wired audio.
