The very first thing I would try is to bring your new TIN into a blank ArcMap session. The current data frame coordinate system may be the reason your TIN doesn't 'line up' with the imagery.
You may have done exactly this but these are the steps I need to take:
Copy a standard esri projection file (.prj) to a new location. For example if your data is in ...
I had the same problem a few years ago. Vector data came in fine but the LandXML was off. I went through some old notes and found how I got it to work, but I had to do it in Civil 3D. Maybe they could modify it for you. The scale will be different I'm sure.
Select the surface/contour (use QSELECT to query)
Type SCALE, enter
Click the surface/...