Sonos Amp and High level input from Subwooder?

The full signal input on a sub is usually for use with amps that don’t have a dedicated sub output. I think you’re better off continuing to use the Amp’s sub output, with the crossover frequency adjusted to suit your sub / your tastes.

In a high level connection you would wire your speaker terminals on the Connect Amp to the speakers as well as to the high level inputs on the Sub.
A cut paste on the alleged benefit of doing this:
"In fact, even if your preamp or integrated has a preamp/subwoofer output, you may want to consider using the high-level connection method. The most prestigious subwoofers in the industry are made by REL of England. They are the “Gold Standard” of the industry and priced accordingly, topping out at $9,000! REL recommends using the high-level input for all of their subwoofers. The reason they recommend this type of connection is as simple as it is logical: it ensures your subwoofer is seeing the EXACT SAME SIGNAL as your speakers. If you use the preamp/subwoofer output from your preamp or integrated, the signal seen by your subwoofer does not include the tonal balance and timing cues created by the amp. By using the high-level connection, the subwoofer gets the same signal as your main speakers, keeping them in better synch with each other, thus improving sound quality."
Easy enough to verify this claim if you have the time and the inclination to experiment.

Sounds like audiophile snake oil to me (“tonal balance and timing cues”), but I guess it’s better to be open minded 🙂

Lol.
More on the theory of high level connections from the speaker terminals on the amp to both the speaker pair and the Sub:

"This might lead you to ask if there is any point using the high level connection, but for some there might be. Firstly there is a subtle difference between the crossover typically used in the high and low level connections. In simple terms, the crossover for the high level connection will usually use a more gradual slope, which in theory could lead to a smoother integration between sub and speakers, where the speakers are full range. This leads to the second important point. Speakers being run in full range mode will not crossover according to the setting in the processor, instead they will output material down to what ever frequency response they are capable of, so this is why the crossover on the subwoofer for the high level connection is more important. The crossover frequency should be matched to the natural low end frequency response of the speakers being used, and this will vary from speaker to speaker. If you are using small sats, then there seem little point in using the high level connection, but if you have larger more full range speakers, then for music this may be preferable. In my own experience, larger speakers will have their character changed when filtered by a processor at 80hz, and this can impact music negatively. If this is the case, then running the high level connection can restore the speakers natural character, while still allowing a subwoofer to improve the low end response, and the end result can be positive for musical listening experiences."

The point about high end being better for speakers that themselves go down deep with enough energy there seems to be a good one.

Again, easy enough to verify and decide for oneself.

Ok, I had planned on getting a Rel sub and the high level connection sounded logical, sharing signal and blending with speakers, but if you guys say the LFE will give me the same signal and sound on the Amp, may not be worth it.

It made sense if lfe was more for home theatre, and the high level for music

Ok, I had planned on getting a Rel sub and the high level connection sounded logical, sharing signal and blending with speakers, but if you guys say the LFE will give me the same signal and sound on the Amp, may not be worth it.

No, high level connections from the amp terminals to both speaker pair and Sub will NOT give the same signal as using the Sub out socket of the amp to the low level on the Sub because the main speakers will now get all frequencies and not just those above the selected cut.
See my two preceding posts.

Also, instead of a REL sub, I would get a Sonos Sub on returnable basis. It does a better job of integration with Connect Amp - and by extension I assume Sonos Amp - than any Sub I have used and for good music play, this integration is very critical.
Let extensive listening sessions then decide if you want to keep the Sonos Sub, after assessing the sound of the existing sub using both high level and low level connections.

Also, instead of a REL sub, I would get a Sonos Sub on returnable basis. It does a better job of integration with Connect Amp - and by extension I assume Sonos Amp - than any Sub I have used and for good music play, this integration is very critical.
Let extensive listening sessions then decide if you want to keep the Sonos Sub, after assessing the sound of the existing sub using both high level and low level connections.

I actually do have a Sonos Sub already, but I had it connected (in the same room) to a Beam and 5,1 setup for movie watching.

I have the Amp connected to two Bowers and Wilkins 685 S2, and a Def Tech Pro Sub 800. I use this for music.

The reason I got the def Tech sub was because I had briefly put the Sonos sub with the 685s, and really liked the way they made the speakers open up.

Not sure I want to get 2 Sonos subs in the same room, that’s why I tried something different with the Def Tech 800 and was considering a Rel Sub.

It made sense if lfe was more for home theatre, and the high level for music
LFE is for movies and is when the Sub is connected to the .1 channel on an AVR. In sound coded for movies, the deep sounding effects are contained in just that channel, which is connected to a Sub for reproducing everything contained therein. If a Sub is not so connected, the channel isn't heard at all - this, from my AVR use back in the day.
The sub out on the Connect Amp isn't LFE; it is a line level output for a Sub after stripping out frequencies above the cross over selected; note that in recording music in stereo, both channels contain all the content, there is nothing separately dedicated to low frequencies. And if nothing is plugged into the Sub out jack, all content will be passed on to the front speakers, with low frequencies then heard from them to the extent of the capability of front speakers to go low.