If you're open for more suggestions on 3D apps, here's my input:
I'm a big fan of AC3D. I've not used it with too many other programs, bar X-Plane. It's easy to use and very easy to learn. The only program easier to learn I've ever used is in a completely different league. That program happened to be Autodesk Inventor.
If you think AC3D sounds interesting, here's a link to the site:
http://www.inivis.com/The license is fairly cheap by comparison to most other programs I've seen; it is a pretty capable program, so it's worth it. It does not have a built-in rendering function but is set up to use POVray. POVray is free and not at all a bad program from what I can tell. The demo is only limited to time, so if you want to try it, you can use any feature you like.
Next is Blender. Blender is NOT new-user friendly. You will need to actively probe the program to get a hold/grasp of all the hotkeys and functions (any program is like that - it's just that it's easier in some programs than others). Fortunately, there's a very large user base so help is at hand. It's also a conveniant platform to use in conjunction with your 3D model and PCS2. I use Blender to import .dae files from PCS2 which I export as .ac files to AC3D... which is all I've had to do with it up to this point. However, if it's your only option, I encourage you to learn it. Blender can be used to render, model, animate, and even program I believe. Did I mention it's a free program? Freeware with a whallop, that's for sure... You'll need to install Python 2.6 or later to get the latest version to run. Python is a free, open-source programming language (which I've never had to use directly, actually...).
SketchUp. I tried the "professional" version and didn't care for it. You'll have to pay for that one. The other version is free, but has been cited to be fairly limited in its operations. However, given some of the SketchUp models I've seen on the board, it's possible to do very impressive work as well. I still wouldn't recommend it, but it's always a matter of preference.
These are the programs I'm most familiar with. Truespace and the EVILLL .cob format only seems to be associated with a very small number of programs for modeling (import and export capacity). Unfortunately the original Volition team seems to have decided that it was what was necessary for the .pof format. Thanks to programs like Blender and PCS2, the pain is reduced in this area. 3DS Max also can be used, though now you're talking about some serious expenditure on software on your behalf. Start small.
-Thaeris