Tom, You will have to use the KEYOUT from the K2/100. The AUX cable will not work with the K2. 73, Don W3FPR On 11/4/2020 10:12 PM, cx7tt at 4email.net wrote: > Question: How compatible is the K2/100 with KAT/KPA500? Is it possible > to connect K2/100 to both of these other units with the K3KPAAux cable > as if it's a K3(s)?