I must thank you all for your patience and help offered, but … I seem to have stumbled across a solution to this problem.
It’s nothing to do with Disketch.app. I didn’t understand how it could have been so.
I found the ‘solution’, which I don’t really understand, in a post on forum dated December 2014 on the BeLight Software site, after desperately Googling the problem. I'd already visited that site once but gave it a second go for some reason - grabbing at straws.
Here's the post I
(by mcaswell) I noticed that when I looked at the printer in the Printers & Scanners PrefPane, it listed "Kind: Canon MG7500 series-AirPrint". It occurred to me that perhaps my Mac was using a simplified AirPrint driver (intended for printing from iPads, etc.), which could explain why the CD print option was not there (since presumably no one would be printing CDs from their iOS device).
I deleted the printer, and then downloaded/installed the drivers from Canon's site (not sure if this step was necessary or not... the drivers may have already been there as part of the OS, but just not utilized). When I clicked on the + sign to re-add it, I selected it from the Nearby Printers list that pops up under the + sign, and noticed that it again was using the AirPrint driver.
I again deleted it, but this time when I added it, I didn't use the Nearby Printers list, instead choosing Add Printer or Scanner. It again chose the AirPrint driver, but I was able to select the correct driver (Canon MG7500 series) in the "Use:" pop-up menu.
Once I did this, I was able to print CDs wirelessly.
Yeah. Me too! I had never noticed a 'Nearby Printers list' previously, btw.
I had also, before the above, downloaded and reinstalled the latest available Canon driver for my printer. It was exactly the same version as had been previously installed. It had made no difference.