Would Sonos Amp blow B&W AM1 speakers?

Unlikely. Are both crackling or only one of the two? You can use the balance slider in the App to find out that.

One of them quite a lot and other is marginal. I bought another pair and they seem fine. I’m returning the original pair to a local repair centre and will update on what the outcome might be. Thanks

 Speakers are damaged via under powered amps and by running them at higher sound levels than they are designed to deliver. Therefore as long as this is not being done, a 20W amp is more likely to cause damage than one that is 100W.

By looking at the damage, the service shop should be able to tell you if excess power supplied to them by the Sonos Amp was the cause.

Is that relevant in this case, I understood the Sonos amp, although not stated, runs nominally at 125w per channel?

It can deliver up to 250 watts per channel if the speaker impedance drops to 4 ohms; it is a powerful amp. A good analogy is a car engine - a small one will always run at close to limits with little in reserve for emergency overtakes, while a powerful one will have power in reserve to get you out of trouble while overtaking etc. But used irresponsibly, the powerful engine can land you in a lot of trouble.

Ah, I think I understand, so I have most likely played music to loud and I have blown the speakers?

With this in mind, is it wrong to pair the AM1 speakers with the Sonos amp is out of balance and is to powerful

Yes, I’d agree, I’ve set the volume limit to 70% already, thanks for the advice

So an update. The speakers were kindly repaired under warranty. One was good the other required the midrange/woofer replaced. Begs the question, now I have  two pairs is it possible/advisable to run them in parallel via the Sonos amp, advice please, thanks in advance.