Given the music mentioned, unless you listen to stuff with a lot of low synth, you don't need a sub.
With my M80s (similar frequency response to the 100) I have switched back and forth between two channel and 5.1 while listening to music. A lot of times I can't tell the difference at the bottom end.
On cds like the ELP debut album where there is quite a bit of low bass synth and organ, I do notice a difference.