Help! My mom got a new surround sound system and I inherited her old Sony STR-DN 1030 receiver that I want to connect to my ev

If your sub is self powered you connect it to the sub woofer out with an RCA audio cable. If it is not self powered and has speaker level inputs you could try connecting it to the front speaker terminals along with the front L/R speakers. You would set the receiver to large fronts, no sub. The better solution is to add an amplifier to the sub but this might not be cost effective.