In article ,
MP wrote:
We have a Garmin GNS430, UPSAT SL30 NAC/COM and Sandel EHSI. I'd like to
add a second course deviation indicator/GS

Don't the 430 AND the SL30 have builtin graphical CDIs? Good enough
for emergency purposes.

If you add a second CDI you should be able to drive it in parallel
with the HSI.

--
Ben Jackson

http://www.ben.com/