How will sound work and how to optimise use of my 2.1 set up

[AllOuttaBubbleGum]

I'm guessing your subwoofer would still be utilized for low frequency roll-off, so even though it wouldn't be able to take advantage of a dedicated .1 channel information from a track which supplies it (distinct and punchier), it would deliver the generalized low end from the 2.0 input for your 2.1 channel system.

This is the way, at least, my 2.1 soundbar handles 2.0 channel information.