I think we might be back to using the Scart adaptor then, I'm trying to remember if the 630v has a headphone jack but age is obviously getting the better of me so you will have to wait until delivery for that one i'm afraid
If it turns out it doesn't all is still not lost as you can get a CYP AU-D3-192 Dac that will convert the optical digital signal to Analogue Stereo Phono that will then plug into the Scart adaptor. I would think you would need to select AV1 on your Sony unit to listen to this feed. Both of these units are easily available online but the company i work for usually has the Dac in stock to pick up. I won't link for fear of advertising.....
However ...
and this is a biggie ... Going down this route may cause some lypsync issues and i can make you no promises either way as it is very dependant on how things all just 'talk' together..
I think it might be worth considering moving onto a more modern flexible system and although i am a little hesitant to recommend specifics there is a large choice of audio solutions that can be tailored to your needs and will be much simpler to use.
I'd be happy to suggest some options if you wish and more than happy if you want to pm me about them.
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Glutton for punishment --- Previously ... 2.6 SD1 x 2, 3.5 SD1, 820S, 820Si x2, 216 Gsi, 220T saloon, 414, 45 1.4 x2 and now a Cowley 75 CDT