@J.Kjerulff 

For the older devices the update can take much longer than for the new ones. But three hours is quite a long time. 
Did you start the update via wifi or lan connection? 
In the update gets stuck and the Sub isn’t already lan cabled to the router directly, please do it and retry the update. 

@Schlumpf 

Thanks for replying mate, Connecting via LAN direct to my router is not an option as my router is in the attic. 

But I got it to do the update simply by trying my iPad Pro instead of my iPhone where the update had basically stopped. 

Next issue was me trying to add the sub to a stereo pared Play 5(Gen2) - I could add the sub to my beam but not the stereo pair of 5s UNTIL I unpaired them and paired them again.. so that was a good 4 hours of trying to do something as simple as adding a Sub Gen 1. 

@J.Kjerulff 

Wow… sound like an adventure. But congrats you did it and thx for your feedback. 

Every once in a while I appreciate the 50 foot Ethernet I got off Amazon for a good price.

Connecting one end to the router in the attic and leaving the coil of cable (bag it to keep down dust issues) in the attic near the access might prove handy for other devices as well as Sonos over time.