Math / cognitive skills is the dimension that has improved the least unfortunately. The brain fog has almost disappeared, which is great, and for short periods of time I feel completely fine. But my problem is that my brain has become intolerant to the prolonged effort required to do math at a professional level. Ideally I should be able to concentrate on a problem for 3 hours uninterrupted, read papers, write equations, etc., but this type of effort gives me strong headaches quite quickly, and even a full-blown relapse if I don't stop. This is frustrating, and this forces me to consider a career change, but at the moment I am mostly feeling happy and grateful about the improvement in my physical symptoms.

About your tinnitus, you are probably aware of this already, but professional ear plugs make a huge difference, as they protect your ears while preserving the quality of the sound. I used to be an amateur musician too and I used these regularly (before PCS forced me to give up on music).