This doesn't cover the Axxess but has a lot of info relevant to what you are doing.
https://www.corvetteforum.com/forums/c5-general/3651226-c5-double-din-install-guide-radio-cd-upgrade.html
The first posting in that link has a how-to PDF file:
https://www.corvetteforum.com/forums/attachments/c5-general/47884863d1431467226-c5-double-din-install-guide-radio-cd-upgrade-c5doubledinupgradepdf.pdf
Here's the first page of it...