what's the question, @herbaceous
yes cambridge has great choral scholarships/tradition - oxford too (I've just spent the weekend with friends whose son is an organ scholar who has been filling me in). The more 'prestigious' the college the harder they are to get, apparently, but it sounds like your DS might not find it that hard given how good he is! They don't confer any more likelihood on you getting into the uni though so people do often get the scholarships and don't get an offer, or get the offer and miss their grades and the choral singing doesn't help and they don't end up going. I know cambridge does instrumental awards as well which are nice to have but not much money. There's a good guide to the scholarships online - i think it might be post offer application for Cambridge and pre for Oxford, but can't really remember.
The more prestigious the college, the heavier the choral workload too, generally.. Some don't mind that, some resent it
DD2 is cautiously looking at Oxbridge too - but she can't decide whether she wants to study music or history/english but she would want to sing and play whichever. She has, i think, done enough at GCSE to warrant looking at an application but I've warned her that actually getting in and then actually getting the grades is very much not a given. It's a lottery of a process.
Other places suggested to her with good choral traditions include Durham and Royal Holloway.
My DH was at Cambridge, I was at Oxford. Neither of us are very musical - but people who were had a wonderful time singing and playing alongside many, many different degrees while we were there. You can sing in some of the choirs without being a scholar.
Orchestras are pretty competitive to get into, but instrument dependent.