7d) Old keyboard instrument fixed around piano bar (7) S?I?N?T (thought spinet, but one letter too many)
16a) ... feel so confused with G&S' sets of notes (8) S?L?E?E?
and
24a) Man following one Schubert piece's style (5) I?I?M
Have tried and tried, but I'm struggling with these last three!
From Wikipedia
'In earlier times when English spelling was less standardized, "spinet" was sometimes spelled "spinnet" or "spinnit". "Spinet" is standard today.'
Thank you all so much. Never heard of solfege (s), but it fits perfectly with feel so g s. I had tried that combination, but didn't come up with anything. Great that you've solved it!