I recently purchased and installed Absolute 3.
Neither Triebwerk nor Symphonic Orchestra show up in the HALion instrument sets menu either within Cubase or in HALion 6 standalone. I tried copying their vstsound files to the Content\HALion\VST Sound folder and rescanning (in Cubase) but no luck.
Both appear in the library manager under the Installed tab. Had no trouble with Dark Planet and Hypnotic Dance, both appear in the HALion instrument set menu and both work fine.