LFE vs High-level subwoofer connection, for FIDELITY

@bartsw in regard to mixing down to mono, isn't bass mono and omnidirectional by nature, so bass should not be evident from a left channel or right channel anyway. It should just be sound pressure in a room.  If you can tell if bass is coming from a right channel specifically or a left channel, then your subs are set up wrong.  I have always been told you should never be able to hear a sub and pinpoint it in a room or it is set up wrong.

@jbuddha882 the answer to your question, whether feeding loudspeaker output to subwoofer adds significantly to the load on the amplifier.  NO, not if you're using a powered subwoofer connected to the high-level terminals. The amplifier is only sending the signal to the subwoofer if it's powered and not added power from the amplifier. Even still let's say you're using a not powered subwoofer, and you are still connecting it to the high-level terminals directly from the amplifiers speaker terminals you should still not have any issues with extra load on the amplifier because once you connect the subwoofer to the amplifier speaker terminals you then connect your stereo speakers to the left and right-out speaker terminals on the back of the subwoofer. Just understand that you must be using an amplifier that is capable of handling the powering of the subwoofer if it is a power-hungry subwoofer. You must also keep in mind that this also applies for if you are running power hungry stereo speakers such as 6 4 2 Ohm. If all 3 speakers including the subwoofer are 8 Ohm you can get by with a less wattage amplifier and will not put added strain on the amplifier and surly, not if your using high impedance speakers. 

@richardbrand  is also 100% right but he explains it in a much more TECHNICAL Manner with less wording than I. He is always very Technical but usually right in his answer.  

@larryincmh 

isn't bass mono and omnidirectional by nature, so bass should not be evident from a left channel or right channel anyway. It should just be sound pressure in a room.

Omnidirectional is not the entire picture, especially in a real room. SPL is exactly how microphones and your ears can localize it. Further, you can localize it by feeling it. You can also localize it from feeling and hearing room distortion. That's from 40Hz that you have to rely on additional senses and clues. 50Hz and above, it's pretty easy to directly localize with just the ear. Now if it's an anechoic chamber, I would say it's hard to localize bass below 80Hz. But in a real room, I say below 40Hz.

You can also confirm the metadata in your music using a visualizer. It will show you a lot of localizable bass from one channel but not the other, or modulating between both channels to create the stereo effect. A good example I quickly use is the intro to the band Soundgarden, Fell on Black Days. There's a guitar solo extending to around 50-60Hz on only the right channel. You can easily pick it up with just the ears in that frequency range. I can upload a screenshot of a visualizer later.

@bartsw so I had to listen to that Soundgarden song on my system. As the song starts I hear the music only on the right channel which is the guitar solo. Then a few seconds in just left of center another guitar comes in followed by drums somewhat in the center and then the entire soundstage fills from left to right. As for the bass what I feel is the pressure in my chest and in the room I don’t specifically hear the low notes from any particular location.   Hopefully the OP doesn’t mind that we slightly hijacked the thread for this conversation.

@larryincmh yes a guitar solo. I was incorrect when I said it was around 50-60Hz. It's actually below 50Hz. And as you stated, you could simply hear it on the right channel. I'll attach a picture of the visualizer on my streamer to show it when I get to a computer. Therefore, if you have an 80Hz crossover using LFE, it will come from both channels instead of just the right. It will be less stimulating and dynamic.