As regards the scholarship amount - MTS only offer a nominal academic scholarship of £200 in the form of book tokens. This is stated on their website and in their prospectus so I'm not quite sure where the 100% has come from. Perhaps this was a full bursary which they do offer subject to means testing. I'm not sure about the amount for music scholarships and we were advised that they were looking for players of orchestral instruments so the rarer the instrument the better chance you would have.
Agree, there is a lot of confusion/ignorance about the difference between scholarships and bursaries. Scholarships are open to anyone and everyone, regardless of parental income and in most independent schools (although not all) are just token awards that may carry other benefits. Bursaries are means-tested awards for parents on low incomes and can be up to 100% of fees in certain circumstances.
My DS did have a pre-audition at MTS with the Head of Music and I agree that you have a greater chance in your child plays an instrument that they 'need' in the orchestra - piano/violin/cello will have to be of exceptional standard for an award. The main thing about the school is that they are so approachable - don't dismiss music until you have spoken to them.