Alphabet associations - I

[Anna]

Phew, Swap the words around: a latin choir (genitive) and the first Roman Emperor

Oh, my Latin is so rusty (I left him outside in the rain) so that is not a clue but a befuddlement to me, never got the hang of gender. Augustus was the first Roman Emperor I think, although I think that is in dispute. Sorry, what was the question again? (It's Friday and I am Frivolous!)
Edit: whoops, Norfy is on the case!

[Norfolk Born]

Isaac Stern

[Flay]

Chori Augustus...?

I've not taken my pills today....

I meant to say: the first Roman Emperor to convert to Christianity

[Flay]

Isaac Stern

fortunately (hides under table).

[Norfolk Born]

Constantine...

[Flay]

Constantine...

[Norfolk Born]

There's a writer called Isaac Constantine...

[Norfolk Born]

Isaac Watts?

[Flay]

There's a writer called Isaac Constantine... Isaac Watts?

Nope. What about the choral bit? In Latin of course

[Anna]

Isaac Casaubon's De rebus sacris et ecclesiasticus exercitationes
Edit: This has no relation to the original questrion whatsoever!

[Norfolk Born]

Nope. What about the choral bit? In Latin of course

Come again?

[Flay]

Isaac Casaubon's De rebus sacris et ecclesiasticus exercitationes

Fortunately not! Choral... (genitive I think!) Constantin... (a Roman bloke so it ends in... )

[Norfolk Born]

...us...? Constantinus? Constantini? Ovaltini?

[Flay]

...us...? Constantinus?

[Norfolk Born]

Heinrich? Is Isaac his first or last name?