I finally made the thumb back/fwd buttons to work using Logitech Control Center 3.1.0. 
Since I couldn't find a similar post in other forums, I thought it would be good to share this one.
To navigate back/fwd I had to tell LCC to map the back/fwd buttons to Left Arrow/Right Arrow and choose the Option Key modifier. Apparently LCC likes to map it to the Windows 'Alt' key but generates the keystroke for the Apple 'Command' key.
Since I couldn't find a similar post in other forums, I thought it would be good to share this one.To navigate back/fwd I had to tell LCC to map the back/fwd buttons to Left Arrow/Right Arrow and choose the Option Key modifier. Apparently LCC likes to map it to the Windows 'Alt' key but generates the keystroke for the Apple 'Command' key.