I own a stereo receiver rated @ 8 ohm with no pre/sub out.I am considering adding a subwoofer to be connected out of the B speaker outputs (not being used) into the speaker level input on subwoofer. The question is ... How will such connection afect the ohm rating on receiver?
The receiver will still be "rated" at 8 Ohms. What load the receiver will be working into will be determined by your main speakers and any other speakers you run from the amplifier inside the receiver. The output to the sub is essentially a by-pass (as long as the sub has its own amplifer) and is not counted into the impedance loading of the receiver.