Thanks for the ideas, all.
Mrs. T42 had malaria in Uganda in the 60s and was treated with atabrine, which left her partially deaf. I have a dip around 3000 Hz, thanks to diabetes - stiffened collagen in cilia, how jolly. Brain very obligingly fills the hole with low-level off-white noise. I don't know if our recent problems are due to further loss or fashions in cinema audio - some films, particularly older ones, are perfectly OK, others are audio pigshit.
Anyway, like most people, if we had 6000€ to spare for hearing aids we'd get something else. No problems forking out a couple of hundred, though.
Centre speaker is already boosted as far as I'd like. Any more and it becomes too obvious that voices are coming from that wee box just under the screen.
Cabling wouldn't work too well - we're ~5m away from the TV with two dogs farting about in between (in all senses of word) and we'd probably trip over it ourselves. Don't fancy festooning it across the ceiling, so wireless it is.
@Jaded, I hear you re AptX - I didn't know about that. A couple of years back we got the Inlaw Paw a remote headset that worked from a mike riding on the centre speaker while we listened directly. Poor bloke heard both with an appreciable delay in between - unworkable. I think the thing got binned.
Think this might fit the bill?
http://www.meeaudio.com/content/usermanuals/UserManual_T1H1.pdfLooks quite decent...