This pretty much isnt applicable for Audiophiles, as I’ve only ever used preamps with at least two sets of outputs and subwoofers with their own amplifiers, but for those with AVR’s, applicable.
For those that have receivers or integrateds with dedicated RCA subwoofer outputs, this post may have some interest.
For the most part, a dedicated subwoofer output on a receiver or integrated exists because of old-school habits. Long ago, at the beginning of the subwoofer era, there were no built-in crossovers. Subs came in two flavors: an unpowered or powered woofer in a box. If the first the user had to supply a power amplifier and if the latter, a crossover to remove the high frequencies from the receiver.
Over time, subwoofer manufacturers moved away from these crude versions to more sophisticated ones with built-in crossovers and amps making unnecessary the dedicated subwoofer outputs.
The problem with this feature overlap between receivers and subwoofers is the confusion it causes.
Without prior knowledge, what user wouldn’t use the dedicated subwoofer output to feed their sub?
The issue, of course, is having two crossovers: one in the receiver and the second in the subwoofer. Double-duty crossovers make for a less-than-desirable outcome.
If you do have a dedicated subwoofer output check with your instruction manual to see if you can disable it or instead, use a Y-connector on the receiver’s main RCA outputs.
Of course, if your subwoofer allows, the best connection possible is from the amplifier’s speaker outputs.
It’s all in the connection.