Thanks,
Visiting some low-end phone and electrical shops this morning, I identified what appeared to be a slightly larger optical plug/cable, but the shop did not know of any different sizes.
The optical connection is identified on the Bluetooth transmitter as 'Toslink'; the connector (plug) as JIS-F05, which is compatible (interchangeable?) with 3.5 mm audio jack plugs, and it this which appears to differ from 'standard' audio connections.
The link has a picture; furthermore the text relating to mini Toslink appears to identify the incompatibility, which if so, then the required adaptor is for the input device, not the tv output.
https://en.wikipedia.org/wiki/TOSLINK
Thus the search is for a 'mini Toslink' adapter - large female optical, not 3.5mm, to small male optical (Toslink) plug; nothing found so far on the web.
The tv output limitation is with the audio jack plug, not usb (my typo).