I stumbled across this reference for a "Simple USB CW and CAT Interface" - http://www.kotarov.com/projects/succi I believe he has sold a couple hundred units. At under $40, it looks interesting. It provides no audio interfacing at all. The user has to have something else to do this, if he is using audio for digital mode modulation. What it does provide is a USB - serial converter, with RTS and DTR "brought out" to drive typical radio PTT and KEY inputs, in addition to TXD, RXD and GND for the CAT connection. This could provide the missing control and CAT signals for those who are struggling to get a SignaLink to do more than it was designed to do. Does anyone know any more about this?