The Sonos ‘Optical to HDMI’ adapter is one way only, so that needs to be at the TV end (Optical Port) and is usually linked to an HDMI cable that goes to the Amp - am I perhaps right in thinking you have the adapter the wrong way around here?

Also the Sonos Connect:Amp has no optical or HDMI-Arc connection… so I’m a little confused?
You might need to provide a little more detail?

50’ TOSLINK is risky and quality varies. I have a 50’ BlueJeans that I used for PLAYBAR and never had any issues. 

Sorry, but the mention of the old Connect:Amp slightly confused me earlier, but If using the new Sonos Amp and presumably something similar to one of these simple pass-through connectors (see below link) with the Sonos Optical to HDMI adapter instead, effectively extending the adapter, it should work, but quality "may’ be affected and undoubtedly you do have to be quite careful with optical cables not to bend them too much etc. it seems some users prefer to convert ‘lengthy runs’ to coax instead.

https://www.amazon.co.uk/Optical-TOS-Adaptor-Pack-TOSLINK/dp/B0B4PVN3FM

This example site below (and others online) refer to 15m as approaching the max distance for optical cable, some sites I saw recommend no more than 10m to not affect audio quality.

https://www.cablechick.com.au/blog/cable-length-guide/

Technically the maximum length for S/PDIF optical is 10m, but it’s usually recommended to limit the run to 5m.

50 feet is likely to be pretty dodgy. It might work with a repeater at the mid-point, otherwise consider using an optical audio extender kit over Cat5e/6 cable.

Thanks for the information.  To clarify, yes, the amp is a newer Sonos Amp.  I didn’t realize they changed the name.  I am going to try a repeater to see if that helps.  I can’t put one midway through since it runs through conduit in a wall.