Hello Moonlight. I actually ran a search function at another extensive forum, looking for both Topfield and Beyonwiz, but didn't post here because the results were very sparse.
When I did find a post or two, it was normally quite favorable. Something like, "Oh I'm having trouble with my provider's DVR, but my trusty old Topfield/Beyonwiz does not have this problem".
Now, personally, I think these devices are a LOT of money, but that being said, when you pay that much, I am assuming that implementation, ergonomics or ease of use are well designed.
Sure, HDMI carries audio. And you can send it to the TV, and that works if she only wants TV audio.
Otherwise, yes you want an optical cable to the receiver. You can also instead run the HDMI direct to receiver, then on to the TV, but YMMV there. It's a worth a shot.
Part of the reason I didn't post here yesterday is because your query seems to be looking for guaranteed assurance, and that is the last thing I can really give you.
But, from my most cursory impressions, you are looking at nice units, and there isn't any reason to think they won't work. Choose the unit that has the feature set you desire.
Oh yes I remember one poster was comparing their Tivo side by side with either the Topfield or Beyonwiz, and they were having color issues with the Tivo.