Hi. It depends on what you mean by “compatible”.  It can almost certainly be made to work.  However, Sonos HT systems, being soundbar based, are really designed for televisions rather than projectors.  The issue with projectors is the distance from where the video originates and where the sound needs to come from (i.e. between the projector and screen).  What sources will you be using?

Btw, advice from Best Buy seems to be produced by a random process and is only ever correct by accident.

The L5G should work just fine. It is equipped with HDMI eARC on HDMI port 2, so the Arc will connect to it fine. The projector also has two extra HDMI ports so you can connect other external media devices like a PS5 or Apple TV 4K.

@Discosupafly,

Yes, assuming the below link is the Projector referred to, then the tech. spec. here looks fine to me to work with the Sonos Home Theatre setup mentioned … 

https://www.projectorcentral.com/pdf/projector_spec_11722.pdf

Thank you very much guys

Update, the install went horribly wrong. The installers 3rd party threw Costco caused severe damage to my drywall, and broke the actual 120” screen. I called Costco had it all taken back and just purchased an Epson LS11000. Luckily the Sonos system was untouched and it’s still in factory boxes. I will be setting up the Sonos myself going forward. 100% assuming the Sonos will work with the Epson without issue

The Epson does seem to have eARC (https://mediaserver.goepson.com/ImConvServlet/imconv/375ac002436a0473a175068677e2d623c77dcba9/original?assetDescr=Home_Cinema_LS11000_Projector_Specification_Sheet_CPD-61059.pdf), so it looks like you’re fine. The Arc does niet an HDMI connection with the projector though. They’re probably quite a bit apart.