I was planning to add some soft key features (Mode X) on the DEK. I don't know the part number but I was assuming that the connection was through the D15. I've seen the setup using the AS-W3 and DEK used by one of those agencies well known for its initials. I suppose that it could be a) a SP kit of some kind, or b)something produced by the agency radio shop. If you are aware of a different setup, please let me know. Thanks.
The only DEK support on an Astro Spectra W3 is in conjunction with the HLN1439 Siren box, and the HKN6145 siren cable with DEK connector. The HLN6096B cable does not have any of the correct connections to host a DEK from the J2 connector. Most likely the setup you saw was utilizing the siren hosted DEK.