With parametric EQ's you can dial into any frequency - I know 20Hz is possible on the BFD, I'm sure you could widen the band to go lower or maybe even dial in lower.

The BFD is usually recommended for cutting frequencies (like most parametric EQ's for bass), but boosting "can" be done if you're very careful. If your seated in a spot where the room is naturally causing cancellations, all the boosting will do is eat up amp power.