Things are coming along (slowly). To test the concept I'm using a Cisco/Sipura SPA3102 to tie the CTX and the Asterisk box. It has a single FXO and a single FXS. So far, I been able to place a call from my DKT extension to a SIP softphone hanging off the Asterisk server.

Going the other direction is going to be a bit more challenging and I'm out of time to play with this for a while.