Promitheas I am using the SH5 steam edition. My steam download came with SH5, bundled together with SH4 and SH3 installations that could be installed onto the PC as well. I have only installed SH5.
The initial SH5 steam installation (vanilla) is complete with all the latest SH5 patches so all you have to do is download TWoS to get the vanilla steam download to upgrade to a real working sub-simulation.
After my initial steam download and install what I did do was run through the opening SH5 sequence to the point where you can see the first vessel to target. At that point I shut down SH5 and re-booted the PC. Then it was a real painless installation of TWoS, following the step-by-step instructions which I printed out.
Hope this info helps you.
