HI, 
I had the same issue, could never get the custom channels to work. I am using the Actisence NGt1 Usb to N2K and it works like a charm. Super simple to use, and works great. 

In the beginning we tried to  calibrate the Garmin system (without luck) so we used expedition as a source for calibrating everything. Now i have bitten the bulled and bought a H5000 hercules cpu. I still use the antisense to display custom values. We just found the TWA and TWD  not as good when sending from expedition - it was jumping slightly to much. I have to say that we are super happy with our current set up. Expedition, H5000 the Garmin Gnx120 displays works really well together.

Yes, in this case, Exp is connected directly to the NMEA 2000 network with the NGT-1.

The NGT-1 will appear as a serial port in Exp.

You can send most data, but the format is fixed by Garmin for most data types.

You will then have two sources of data to Exp - theNGT-1 and the H5000 websocket. It is a very good idea in Exp to
1. Disable GPS data from the H5000 (there is an option on the Exp connection page)
2. Enable only GPS and AIS data from the NGT-1. If you have more than one GPS source on teh network, you can tell Exp which one to use.
3. Enable the Garmin PGN Tx option in Exp.
The GPS data should have lower latency into Exp this way.

Slight tangent, but issue relates to getting GNX120 to work with H5000.

I have H5000 and Zeus, etc. and GNX120 shows different “cryptic” numbers (mainly 9-digit decimals) for me to choose between as potential data sources for various parameters (GPS, NAVIGATION, HEADING, BAROMETER, ALTITUDE, etc.)

For some like BAROMETER it’s easy because it shows only one 9-digit number. However for GPS and NAVIGATION it shows multiple 9-digit numbers. After a bit of faffing and head scratching, I found I can deduce which 9-digit number is which by removing all the blade fuses on the switch panel, and then re-inserting them one-by-one … tedious, but Garmin don’t seem to know a better way … so I’ve now mapped one 9-digit GPS source to NAIS500, another to H5000 another to Zeus.

However, for WIND the GNX120 offers 3-4 9-digit data sources, all of which ultimately flow from a single WS720 wind sensor (connected as analog port to H5000). Hence, as would be expected, all those 9-digit numbers appear/disappear according to whether the blade fuse for the H5000 is inserted/removed.

I speculate that the different 9-digit number map to subtly different wind calculations (like True Wind and Ground Wind), but does anyone know how to decipher which 9-digit number maps to which ‘type’ of wind?

I use a laptop to publish BSP and Heel Targets to my GNX120s via Actisense and Garmin Custom Channels.  Is this the best practice?  I don't believe I can send them via my H5000 Herc to the GNX Displays.  

Is there a way to change the dampening and precision that are displayed on the GNX120s?  The dampening I apply in Settings>Channels does not appear in the GNX Displays.  From a quick read of the GNX manuals, it doesn't look like their dampening feature applies to custom channels.  Am I missing something?

My objective is to get Target BSP displayed with 1 decimal precision and damped x seconds.  

Thanks in advance for any tips!