Hi Nick,
It does make a difference in helping with those lower frequencies that the AVI's don't produce. However, I only really use if for movies nowadays as I am very happy with the generic sound of the AVI's.
I have not tried any other subs as I have been very happy with this one for years now. However, when funds allow sometime in the distant future, I will try out the AVI sub.
** And to the OP, do you have a budget in mind??