Any bass preamp will work. Connect to the aux-in and you're all set.
But if you plan to play along to recorded music my advice is don't do it. Very hard to get everything sounding good and avoid creating mud and phase cancellation with the recorded bass track.
IMO it's much better to have separation of the two systems. That way you can change the balance of what you hear simply by taking a step or two to in one direction or the other.
One vote here in favor of a dedicated bass system of some kind.