A:
There's no built in place to plug in a powered sub-woofer, so you'd have to bake up a solution on your own, not hard if you have any electronics training.
But there's always the question, "How much bass do you need?" I've never found a published value for the frequency response range on these speaks. However, out of curiosity I ran several speaker response test from YouTube to test my own Bose Companion 20s. (Full disclosure, I wear hearing aids so my perception is a bit skewed.) I was pleased the speakers kicked in at around 44 Hz and climbed steadily to above my hearing range at about 15,000 Hz.
Past all that I've been quite pleased with these speaks. The clarity is very good, HiFi quality good. These replaced the top of the Logitech line speakers with a subwoofer, I was fearful the Bose wouldn't match the performance of the Logitech which was quite good, with deep bass. I have not been disappointed with the Bose and they lose less that 10 Hz on the low end, but more than make up for that in the clarity and separation.