I bought a new sony receiver with no sub woofer output so when i plug my subs into it i have to turn them down manually they wont turn down using the volume control on the receiver
More details would help (model of receiver and sub).
If you have connected your subs to the record output of the receiver the volume of the sub would be constant. If you use one of these http/www.crutchfield.com/p_142LOC80/Scosche-LOC80.html
connected to the same speaker terminals as your front speakers you can connect the subs to it and the volume will be adjusted along with the speakers. It does not affect the power or performance of the receiver.