The G could be a useful feature to define the brand - could be used on its own on concert posters (e.g. big swirly G)
If strapline is used on logo is must be legible when logo appears in the top of web page.
Convey old and new? One possibility is a swirly calligraphic 'Gaude' but still looking modern and professional, not old fashioned. Equally a striking modern font could work, but it needs an interesting 'G'.
No musical notes! Very cheesy!
Good examples of professional choir branding are:
https://www.sonoromusic.com
http://www.exaudi.org.uk
http://thesixteen.com
Gives an idea of what we would like to stand out against - something new and fresher looking than these?