That very much depends on what audio ports the PJ has. It needs eARC, ARC or optical (in order of preference). Some have none of these, in which case buy a new PJ.

Note that one pair of speakers (likely the Amp with its connected speakers) will need to be a separate ‘room’ than the Sonos Home Theater ‘room’. Which will mean synchronized playback with streamed content, but the PJ input will be delayed by about 75 ms on the ‘grouped’ room. 
 

The Sonos Arc supports a single pair of bonded surround speakers, you do not have the option to add more. 

Thanks Bruce .

just to confirm I can’t run multiple speakers with amp in home theater ?

My projector has the HDMI option 

Your room options are

Option #1

• Arc + Sub + Amp and wired speakers as surrounds
• Era 300’s as a separate room

Option #2

• Arc + Sub + Era 300’s as surrounds
• Amp and Wired speaker as a separate room

With any option the rooms can be grouped to play in sync for music. However, grouping of rooms for TV audio will causes a 75ms delay for speakers outside of the Home Theater (projector).

The challenge with any projector and a Sonos soundbar, while frequently is ARC/eARC, often ends up being placement. The Sonos soundbar wants to be at the front, the projector wants to be at the rear. It may be why Sonos doesn’t advertise any projector compatibility, at least that I’m aware of. It frequently requires extensive HDMI length, which could be beyond standards for an ARC (Audio Return Channel) signal.

Unfortunately, I’m not familiar with a home theater speaker system designed for use with a projector, which isn’t to say there isn’t one out there. I do know Sonos doesn’t currently make one.