I'm using an old copy of FeatureCAM 2007 that was included with my first Interact which had a TNC151B control. That machine sadly was lost in a moving accident, but I now use the same software with my TNC355 equipped Beaver Partsmaster. Generate the tool paths and post process them into Heidenhain conversational code and use Heidenhains TNCServer to upload them to the control. TNCServer is part of TNCRemo, which is a free download from the Heidenhain.de web site. FeatureCAM has many post processors, and will do H conversational, and H ISO G code with equal ease if you have the magnetic keyboard overlay for your TNC2500. It also allows you to tweak the post processor, so I have adjusted mine to cope with the 16 station tool changer that I have.
You have a TNC2500 as I understand it. Never used one, but I believe it was essentially a TNC151/155/355 rebadged for Bridgeport
Andrew Mawson
East Sussex, UK