I have a single ksf 8.5 I picked up for $20 and have a chance to get a ksf 10.5 for $50, will they sound ok as a pair? I know the 10.5 has an extra 8" but dimensions are close along with wattage. I'm going to look at a pair of 4.2 today, if I buy maybe 8.5 becomes a rear center? If not will the two different speakers sound horrible together? Please help! Thank you