Him wanting to stay at a particular college with his mate and his inability/unwillingness to find a college with a more suitable course for him despite transport issues is actually a problem. He is going to be competing with others who are dedicated to music whether as he's already demonstrating that not the centre of his world. That together with incredibly poor guidance from the school puts him into a position where I would be saying, you really need to start having some very difficult conversations with him.
He either gets his head down and gets that Maths to a low grade rather than a U to demonstrate he's really committed to uni to have a chance of getting something, he finds local experience of music production and he does that as work experience over the next year, finds a suitable bridging course like a foundation course or he starts to have a reality check about his chances in this field and considers what other options may be available to him. If he's prioritising his mates and he (and you) are not trying to over come practical barriers like transport, this isn't the gig for him as honestly it's just so competitive and his heart isn't going to be in it enough. That's the bluntest reality there is.
When you get to 17/18 you have to start looking past a future with your friends and beyond that being your whole world. You need to be looking past your mum and dad giving you lifts everywhere. Those friends probably won't be seen for dust come next September and he doesn't want to be the one being left behind. He needs to start making some choices about what is best for his future without clinging on to mates who won't be there much longer. Is he learning to drive? Is he working part time to save to learn to drive or to get a car? This stuff matters.
Why?
I'm detecting an element of a lack of maturity showing. Even the decision to do maths has a bit of that thrown in because he didn't want to do the performance element of music. It's an abdication issue where he doesn't want to put himself out of his comfort zone. The music industry is rough and requires an element of being almost slightly pushy at times. The kids who are super confident and super determined are the ones that will succeed in this field.
If that's really not his personality it's time to start being a little more honest about this and to start looking at other long term pathways or shorter term things that he's interested in and will at least give his a job chance so he can develop his skills in music as an additional thing rather than his primary career choice, in order to give him more confidence and more time. (See my previous comments about the lad who dropped out and worked his arse off in bars - this gave him opportunities to do the music production at those venues on the side and also allow him to learn to drive and having money coming in and not looking like a bit of a lazy waste of time). You can't be continuing to be doing all the leg work to find out what options and alternatives are out there. He needs to be proactive and participating in FINDING what he can do. He needs to be getting on Google and asking advice on music forums about how to get ahead.
It is better he recognises this, this year, rather than you get stuck with a disappointed lump at home who doesn't want to do anything and doesn't have a job or a course to go to when he doesn't get the grades he needs in August. That's the worst possible outcome. Something is better than nothing and not doing his dream job.
This is crunch time now - I know kids who have been in similar situations where it's actually been a real blessing to be in this position now and they've been able to get their heads around it and actually ended up in a better position than some of their friends who were predicted much better grades but then flunked. So don't think this is an absolute disaster. You have a little time to help him make some sensible proactive choices - but you need to be realistic. Be ahead of the game on this, rather than letting this fester for the next 9 months or you are going to have a disaster on your hands.
I wouldn't be quite so harsh or negative about every career path - but anything to do with performing arts, music or media really is like this and you need to know when you set out what you are going to need to do.
There are various different paths - he needs to find the one that's the best fit for him.