With the release of Pro Tools 2020.6 in June 2021, there is no longer a 32ch I/O restriction for non-HD interfaces.
Previously if you wanted to use two Apogee Symphony I/O or MkII units together for up to 64ch, you had to connect with a PC-32 cable to an Avid HDX or HD Native card.
Now, the HDX or HD Native card is not needed. Any Apple CoreAudio interface can get up to 64ch of I/O. This allows Apogee customers to enjoy full use of their superior Symphony I/O converters with Pro Tools.
See this article for more on this new Pro Tools software release: https://www.avid.com/resource-center/exploring-increased-voices-tracks-and-io-in-pro-tools-2021-6