You can even try a trick I learned somewhere, treat the cloth surrounds with brake fluid. It may seem odd but I used this method on the woofers in my JVC PC11, the surrounds were so hard that the cones could barely move, after a couple passes with a q-tip wet in brake fluid (I bought the cheapest and smallest bottle I could find) they are transformed, now the cones are free to move and the sound improved a lot. Consider that I did this 5 or 6 months ago and the surrounds are still OK, so no harm to them.