Just purchased the xtrend 8500 i have two cable tuners in A & B i have my coax plugged into tuner A i have then plugged another coax looping from tuner A out to tuner B in. I assume this is right?? when recording i can only FTA on tuner B is clear if i put a sub channel on it isnt clear and it normally is using tuner A normally. Any ideas why this is?