Any main output from a preamp will work to the subwoofer line in (high level input). Many preamps have a pair, or more, of stereo main outs. This allows the preamp to drive up to three stereo amps in a bi or triamp mode or to drive an amplifier and a subwoofer.
Many subwoofers only have ONE RCA line level input; ie, no stereo inputs. In this case you just get a 2 into 1 RCA adapter and then run one RCA interconnect to the subwoofer. Monster Cable makes a decent quality adapter. In fact, I have several of them I no longer use and would sell for about ten bucks. The Radio Shack type things are real junk.
Most subwoofers also have speaker inputs. All you do is run an extra set of speaker wires from the amp speaker outputs to the subwoofer in addition to the speaker wires to your main speakers.
Many subwoofers will offer a line out or speaker out and these outputs are intended to allow you to simply put the sub between your amplifier and the main speakers and you route the high frequencies to the main speakers and only the low frequencies to the sub. Typically, this will allow small main speakers to play louder and with less distortion. That is the good news; the bad news is that most crossovers inside powered subwoofers are junk and not to be used as it adds another active stage to the signal that has already been amplified by your amplifier. Best method is to run the sub in parallel with the main speakers. Another method is to acquire a quality active crossover and not use the internal crossover of your sub. Of course, in order to do this effectively your sub would have to have a way to defeat/bypass the internal crossover.
Hope that makes sense.
Many subwoofers only have ONE RCA line level input; ie, no stereo inputs. In this case you just get a 2 into 1 RCA adapter and then run one RCA interconnect to the subwoofer. Monster Cable makes a decent quality adapter. In fact, I have several of them I no longer use and would sell for about ten bucks. The Radio Shack type things are real junk.
Most subwoofers also have speaker inputs. All you do is run an extra set of speaker wires from the amp speaker outputs to the subwoofer in addition to the speaker wires to your main speakers.
Many subwoofers will offer a line out or speaker out and these outputs are intended to allow you to simply put the sub between your amplifier and the main speakers and you route the high frequencies to the main speakers and only the low frequencies to the sub. Typically, this will allow small main speakers to play louder and with less distortion. That is the good news; the bad news is that most crossovers inside powered subwoofers are junk and not to be used as it adds another active stage to the signal that has already been amplified by your amplifier. Best method is to run the sub in parallel with the main speakers. Another method is to acquire a quality active crossover and not use the internal crossover of your sub. Of course, in order to do this effectively your sub would have to have a way to defeat/bypass the internal crossover.
Hope that makes sense.