I have Helix 10 MSI G3N (v 2.110) connected via Ethernet with the laptop and I use AutoChart Pro v2.300 (Released on 15/06/2018).
Unfortunately, AutoChart Pro cannot obtain live images using the MEGA frequency.
Functional only with 455Khz and 800Khz.
In October 2019, I opened a link on the Humminbird website and was informed that, unfortunately, they had no plans to make AutoChart Pro compatible with live images on the MEGA frequency.
So far, Humminbird has not made any updates to the AutoChart Pro software which is out of date in my opinion.