I had a think about Kath’s message and looked on the v6 TiVo box. Under audio there is an option for Dolby 5.1 or stereo. It was set to 5.1 so I switched to stereo. I didn’t expect it to make a difference but it did. Sound now works on the iPad.
however I’m disappointed that this setting isn’t specific to the equipement directly connected to the TiVo box rather than streaming to the Go app. Surely you can fix this VM?