I realise this is a bit of an "old chestnut" topic, but thought my experience may be of interest to anyone going this route.
Had a rather nice Xmas present of Sennheiser RS 175 wireless phones.
These have a digital optical input (cable supplied) as well as the usual analog inputs. Wired this to my Sonos Connect optical output (the Connect is powering my conventional Hi Fi system)
The result is very pleasing, works a treat with Sonos. The sound quality is all I could wish for & the range seems more than adequate for our 3 bed house.