Thanks for the quick reply!
Other than the SL30 and GNS430,530,etc type NAV receivers, are there any others that will provide guidance on the D100 ie older/less expensive receivers?
Not really. We'd designed the HS34 HSI expansion module with analog inputs/outputs for just this use case, but it turns out that those "standard" analog inputs and outputs are anything but, and so unfortunately we don't have support for legacy NAV
radios.