I did this mod yesterday. I used the 220uf because Radio Shack had them. (they have no clue if they're polarized or not but thanks to Maxcichon I knew it didn't matter) They cost $1.69 each. I have to agree that the change is noticeable and an improvement. However, I'm going looking for the 270uf. I think the 220's cut a tad too much bass to the front speakers. I'd recommend adding wire length to the capacitor beforehand so you have more slack to make the connections. (as suggested by others) The access panel is tiny and there is little room to work with.

All said and done, thanks to all that have contributed to this thread for a simple, dirt cheap way to improve the sound of the stock system.

Les