I currently am using a HK 2.1 5 channel amp to power 5 4.0 Norh ceramic speakers. I also have a Rava sub. I am using a Yamaha rxv-800 receiver as a preamp. The crossover on the Yamaha is preset at 90 hz. My question is I really wany to lower the crossover point to 80 hz. Is there any way to bypass the internal Yamaha crossover? What type of difference in sound will I hear by changing the crossover to 80hz? I have also noticed that there are two preamps available on Ubid and Ebay, that I can buy at approximately the same cost I should be able to sell my Yamaha receiver for. They are the Sherwood avp-9080, and the Harman Kardon 2.1. Does anyone have any thoughts on either of these? Thanks.