Hi @speabody
Welcome to the Sonos Community!
As that projector has no HDMI-ARC socket, low latency isn’t going to be an easy option with a Sonos Amp. In order to prepare audio sharing and synchronisation on the network for multiroom playback, the Line-In input of the Amp is delayed by at least 75ms. The only way to bypass this is to use the HDMI socket on the Amp, and that expects a HDMI-ARC signal from the display device. The HDMI input is not prepared for multiroom playback before being passed to the amplifier circuit, so is much quicker to play on the Amp (and Sub and Surrounds, if connected).
The easiest way to get stereo audio would be to use the Line-In on the Amp and adjust the audio delay on the projector to re-sync the audio and picture (you’d need to advance the audio, which may be described as a negative audio delay). Any other Sonos device on your network could play this feed, in sync.
If the projector doesn’t have this audio delay adjustment option, then you’ll want to use HDMI and will need a device like the HD Fury Arcana (not supported by Sonos, but many in the Community use it successfully) to provide the HDMI-ARC signal the Amp requires. The advantage of this is no lip-sync adjustment will be required and you’ll have the option of playing Dolby Digital 5.1 audio tracks (and DTS soon).
A Sonos Arc or Beam (Gen 2) would need the same HDMI-ARC feed, but they can also use eARC to support higher-quality streams, like Atmos (compressed Atmos is available over ARC, but the Arcana supports eARC and you’d need one, so this is beside the point). Neither the Beam nor the Arc have RCA Line-In, so the audio output on the projector would not be of use.
If an Arc or Beam were used, the Amp (or a pair of One SLs) could be bonded to it to provide surround sound. If the input is stereo, then you’ll only hear a little audio coming from the surrounds, not the same audio as the soundbar plays.
I hope this helps.