Forsey, I know this is an old topic but were you able to get this resolved? I just purchased a bike with the Pioneer PM and am experiencing the same issue.
Thanks,

****Update****
I followed the advice from the other post and was able to resolve my issue. I purchased the Pioneer SGX-CA500 and was able to switch it to ant+ mode. I have the SGY-PM910H model. If the meters were purchased later than June 2015, the Pioneer computer is required to switch the mode. I had to manually enter the device number to be able to update the firmware. I included links for the firmware update process and the installation manual if anyone else experience the same issue. I'm now able to pair it with my Garmin 530.

Firmware update:
https://www.pioneerelectronics.com/...0Update%20Manual.pdf

Installation manual:
https://www.pioneerelectronics.com/...llation%20Manual.pdf