Yes to both; you can select the crossover that is appropriate given the nature of your main speakers.

Small edit; the amp does not auto detect the Sub, it has to be added to it by you via the app.

Thank you for clarifying. Do you know the crossover range? Can it go below 70Hz? 

I remember it to be 50hz to 100hz. Maybe even 110.

If it's 50Hz that's awesome. My speakers can go down to 40Hz so maybe a 50Hz crossover would be good, despite the 80Hz THX standard. I'll test it. 

Thank you Kumar. 

50 Hz makes sense if they go down to 40 with just a -3dB drop, and not -6dB. Specs can be tricky. In the latter case, 60 to 70 Hz crossover may be better to allow the Sub to contribute more at those points. 

But test and decide, since it is so easy do this via the Sonos app.

Hi Kumar. My system is yet to be set up, my Amp is on the way. 

Someone frightened me by saying that stereo amplifiers cannot adjust a crossover for the main fronts. In other words, should I set Sub crossover to 80Hz then the speakers will kick in around 45Hz and play together with the Sub until the Sub fades at 80Hz.

Is this true? Or can the Amp configure Sub to play till 80Hz and speakers only from higher than 80Hz? 

Thanks for your time. 

The sub will also be the Sonos one? 

Sure. 

Sonos Sub, Sonos Amp, Wharfedale Diamond 8.2 (passive books). 

Then don't worry at all. The Sonos sub will integrate very well. The amp will move frequency below the crossover set from the main speakers to the sub in a seamless way via the slopes on the filter. If your sub will be placed somewhere between the two main speakers, I suggest starting with a high crossover as a starting point for the tests.

Thanks Kumar you're a true Sonos hero. 

With Arc the best placement for Sub is to the left of the left speaker angled towards the center MLP. It sounded terrible in the middle. 

Can't wait to get the Amp... The Wharfedales should be awesome too, especially in my small room. 

Try the middle with a 100hz crossover and go from there. In the middle the fact that humans can locate source of sounds down to a frequency of 80hz won't matter.

Also play with the sub audio level to see what suits best.

In my case, I now have Sub doing bass for a play 1 pair. There is no Sonos published spec for the fixed crossover level in this set up, but it is reported by some to be about 96Hz. With the Sub placed midway between the pair, it works very well; of course the advantage in this set up is Trueplay tuning which is a big help in getting the Sub sound corrected for the listening position, tightening up the bass and eliminating bass bloat.

Although your speakers may go deeper than the play 1 does, removing low frequencies supplied to them will allow for a better job of reproducing the remaining frequencies. This difference may be subtle, but noticeable as better mid range clarity.

Since automated tuning is not available to you, play around with things till you get the best results. By things, I refer mainly to Sub placement, crossover selection and Sub audio levels. But first make sure that the main speakers are placed as well as they can be to allow them to shine.