You are right. TrueSpace cannot handle big scenes as it can't use more than 2Gb of RAM. I've tried the 4Gb patch
and it doesn't seem to help.
VRay is multithreading because it operates through the Bridge.
3Delight as a standalone renderer is supposed to be multithreading also, but I don't know if Dribble allows for that. Clinton may know...
If Dribble is a bottleneck, then the RIB export may allow us to use an external renderer.
Now regarding other standalone render engines, I like Marmost Toolbag 3
interface very much. It is not expensive (132 $ with Black Friday rebate), it handles large scenes, provides with real-time rendering, offers full control over the camera, lights, etc... In brief, it only does rendering and that's all I need !
It loads OBJ files from trueSpace as Xrefs. It means you can continue to edit your mesh in trueSpace, then save it in OBJ format from time to time, and Marmoset updates the model in real time. OBJ format keeps the location of your object in the 3D space, so you objects loads in Marmoset at the exact same location as they are in trueSpace. There is no 90° flips or so.
It's almost as simple as switching from Model side to Workspace...
The only issue with OBJ is about shaders. You have to edit each shader manually in Marmoset to match what they look like in trueSpace. If your object has textures applied, basically, you have to open the Emissive panel and make sure color is set to white and glow to black.
I've got an old conversion program called Deep Exploration (it's like Polytrans) that loads entire trueSpace scenes (just have to make sure I save my .scn in tS4.3 compatibility mode) and converts it in Collada format.
Marmoset load Collada pretty well. All textures and shaders settings are saved, even lights and cameras locations (there is only a 90° rotation bug for the cameras) !
With an FBX or COLLADA export plugin in Modeler side we could have a seamless Bridge with Marmoset of similar tools...
Clinton, are you reading ?