Steam has recently (in the last few months) added the ability to install your games to any drive, regardless of the drive that Steam is installed on. That doesn't help you with DRM, but at least you can manage your capacity between your SSD and HDD. Steam also lets you back up your game to a user-defined location, should you choose.
Personally, I don't like having to remember where my disk and key are located, or having to go through the effort of inserting a disk (as lazy as this sounds), so I love Steam for the convenience it offers. Automatic cloud backup of my save games is another big plus. But, to each his own...
I have my Steam install on a separate 2TB drive rather than the SSD. Whatever it installs goes to the 2TB.
How to move a Steam installation