I have just purchased the PEAVY DTH S5 Concert speakers and they are great but I was looking to replace the 8" speaker with a 15" My first question is can I do this? and if so what specs are needed for me to make the 15" to play in the cabinet? When I just swapped the speakers out I got no sound and just need to know what else i need to have to make the 15"(made by harmony) work. any advice would be appreciated