I've recently moved from Lync to S4b on a Mac running Sierra. With Lync, I had an option to transfer my audio to my Avaya PBX Speakerphone. It was done using the button hilighted below. The nice thing about this was that Skype understood it all and I didn't show up as 2 separate attendees in the call and sometimes it improved my audio experience.
Does anyone know how I acheive this in S4B. I know it took a configuration change on a server for it to work for me under Lync but I don't see anything resembling this on the transfer screen (which is always disabled during meetings.)