Hey, just wanted to pitch in here (not really a part of the community, but found this page via google search - seems pretty awesome!) I’ve just integrated the INS output of the inertialsense EVB as a GPS sensor to the Pixhawk GitHub - inertialsense/Firmware at inertialsense. I haven’t done the IMU or replaced the internal estimator yet, though the inertialsense’s ins output is superior to the pixhawk.
It’s a really cool sensor (statically and thermally calibrated dual IMUs), and the dual magnetometers are robust to magnetic interference, so it might do okay while under water for short periods. I set it up so we could do RTK via QGroundControl, but I’m wondering if the integration would help you guys out at all.