Who told you the Amp wouldn’t have sufficient power? According to the specs, the Rubicon 2 has a speaker impedance of 4 ohms with a recommended amp power of 40-150 watts. The Sonos Amp can send 250 watts per channel to a pair of 4 ohm speakers.

https://support.sonos.com/s/article/4717

I know. I also found the same. It was my local hi-fi dealer who told me. I would not risk destroying my new speakers. So I ask if someone has any options that might work better if I can not use the Amp. 

Never believe audio salespeople.  They lie more than used car salesmen.  Let me guess, they recommended some audiophile level amplifier?

It doesn’t seem fair, but lower powered amplifiers damage more speakers than high powered amplifiers. If you gave me a job: “please blow up this speaker”, I’d pick an amplifier in the 50W range and give it an 80-100W job. It won’t take long and I’ll damage the tweeter. The amplifier will enter a mode known as “clipping” and this generates much more high frequency energy than naturally occurs in music -- damaging the tweeter that was designed with the natural music energy balance in mind. The absolute last amplifier I would pick is any SONOS product because they are designed not to enter this clipping mode. 

AMP should tolerate the Rubicon 2’s very nicely.

If memory serves me well “not enough power” was a complaint about the old Connect:amp that Sonos wanted to solve with the Amp.

A bit of tech: The “impedance rating” of a speaker is a judgement call by someone. A speaker’s actual impedance varies instantaneously with frequency. Sometimes the rating assigned is the absolute low point that typically occurs in the 60Hz range. Other times whoever makes the assignment will pick an “average” (unspecified) frequency in this range, measure the impedance, and assign this number, but there could be a lower point (typically) below this frequency. Very high end speakers are notorious for having one of these low points. The result is that a very low note, say 30Hz, might present a 2-Ohm (or lower) load to the amplifier. Some high end amplifiers will tolerate this better than modestly priced amplifiers because the expensive high end amplifier might have originally been designed as a (much more expensive to produce) 2-Ohm amplifier. Certainly, if this high end amplifier is paired with a speaker that exhibits a 2-Ohm dip, the amplifier will sound much better on that very low frequency note.

Earlier SONOS amplifiers had very stern limits and would instantly shut down if the speaker impedance slipped below 4-Ohms at some frequency. This is a great feature and, as described above, protects both the speaker and amplifier from abuse. AMP is a more flexible, intelligent design and will tolerate brief dips below 4-Ohms without raising a fuss, while also preventing clipping. If you try to fake out AMP and connect a speaker that really should be rated bellow 4-Ohms, AMP will figure this out and shut down.

I don’t have experience with the whole universe of speakers, but I have not been seeing reports of AMP balking while driving speakers that are known to fluster amplifiers.

Thank you for your elaborate answer @buzz , much appricated. Sounds like I can give the Amp a try. Can’t wait to try my new speakers.