The Beam (Gen 2) can connect to TVs with HDMI-eARC, ARC, or optical outputs. For greatest compatibility, eARC is recommended.

Note: a regular TV HDMI port cannot be used to connect the Beam direct to the TV.

• If you connect to a TV with eARC, the Dolby audio formats supported include Dolby Atmos, TrueHD, MAT, Dolby Digital Plus, and Dolby Digital.
• If you connect to a TV using ARC, the Dolby audio formats supported are dependent on your TV model and manufacturer. The TV may be capable of sending Dolby Atmos, Dolby Digital Plus, and Dolby Digital. An ARC connection cannot support TrueHD or MAT.
• If you connect to a TV using the optical adapter, the Dolby audio formats supported are dependent on your TV model and manufacturer. The TV may be capable of sending Dolby Digital. Note: An optical connection cannot support Dolby Atmos, TrueHD, MAT, or Dolby Digital Plus.

Thanks for that but do you think that with the Sonos being 3 channel and my Yamaha a 2 channel if I connect it to the same input then I may notice a difference 

I guess 95% of what you hear over TV will be PCM or PCM Multichannel (2.0 to 5.1), Dolby Digital, Dolby Digital Plus (up to 5.1) audio output to the available Beam speakers. 

It depends on what codecs your TV supports, aswell as the original audio sources, Apps etc.

If you connect to a TV with eARC however, the Dolby audio formats include TrueHD, MAT, Dolby Digital Plus, Dolby Digital and Dolby Atmos (128 sound objects embedded in the Atmos metadata stream)

So these things may depend on the TV Hardware, aswell as the audio source. I’ve not heard the Yas 306 Yamaha bar, but if it’s limited to 2 channel stereo, then I suspect the Beam will be an improvement anyway, but the answer might be to perhaps listen to the Beam in store, or you could buy direct from Sonos online who offer a 100 Day return policy which you can read about HERE.