DC-09 is an open standard from SIA that we support but only a small number of central station equipment manufacturers support it.
If your Envisalink is branded from Eyezon, then your module uses the proprietary Envisalarms service. If you received it from your security dealer or your alarm monitoring company, you may get DC-09 or one of the other "closed" formats that we've been forced to support. It depends on the central station.
It would be nice if everyone supported DC-09 but alas that situation doesn't exist today.
DC-09 would be a poor choice to build an interactive service around. It is simply the same alarms that are sent on your phone line, but over IP. There's no extra information, let alone any control.
It would make a lot more sense from my point of view to design proxies and middleware around that interface than the tpi, since it should be the same for any standardized ip reporting system, not just this one.
Envisacor created to the TPI to provide direct access to the module for developers. Considering the level of support we have from HA vendors, it is arguably the de facto standard, at least for DSC panels. You are probably safe developing with it.