I have just recieved 4 new Bass Shakers, I am now in the market for a amp to power them. Could someone out there please tell me a good amp to use for these? They require 25W per unit and are rated at 4ohms. I am not sure if I should use them in series or parallel, so I can use some help with that question too. There are a couple of "posts" that refer to amp on the Parts Express website, but the links do not work. Thank you in advance.