I am thinking about buying the JBL SB 350 or some other 2.1 channel home theater speakers, but since I have never owned such set up I don't know if YouTube, Twich, SolarMovies, Spotify ect support 2.1 channel audio.
The soundbar can't reproduce bass so if you send stereo audio (2.0) to a soundbar/subwoofer system it will remove the bass from the stereo channels, send the upper frequencies to the soundbar, and send the lower ones to the subwoofer.
Music is never recorded in 2.1
Many PCs don't have a 2.1 output mode at all.
Only movies (and maybe games) have a .1 LFE (low frequency effects) channel.