I've extracted the Xbox 360 version of Trials Evolution, and it seems to contain both normal textures with a T5X header and atlas textures with a T8X header. The T5X textures were simple enough to convert: I just read the 4-byte magic number and two int16s for the dimensions, then skipped to offset 0x1D and read the rest of the file as DXT5-compressed data. However, I haven't had any luck with the T8X textures yet. I've attached six of them for reference, though I have more if needed.
T8X Textures.zip