1) We spent quite a bit of time with AGTEK Support about this, and the person we were talking to (who seemed very knowledgeable) wasn't aware of any utility.
2) That didn't seem to work either.
I have a work around, but it's a frustrating one. Basically I create pionts along the 3dpoly lines every 1' or so. Export the points to a text file, and import them into AGTEK
I was just speaking with someone at AGTEK and I mentioned your issue. The person I spoke with told me that AGTEK support has a seat of C3D and support should be able to get your surface into AGTEK ... but they suggested that rather than trying to get the C3D DTM into AGTEK the solution might be to export C3D's breaklines and other 3D linework to DWG, then import that into AGTEK and let AGTEK generate the TIN. I don't know who you spoke with in tech support, but I'm told Greg Klose is the AGTEK technician most familiar w/ C3D--perhaps you should upload your C3D data file(s) to Greg's attention and see if he can come up with a series of steps that will work for you.
My pleasure ... I hope you will post the specific steps here once you have the details worked out!