It's the latter.Not sure if I understood:
- Only one of the installed PHP versions will be able to run as DSO?
- Or if you install, by example, PHP 5.3 and 5.4 you can set 5.3 to be DSO and 5.4 to use fastcgi? (beisdes that, I know it could use tons of RAM, and the UI should warn about that)
Only a single DSO can be in memory at a time (without some trickery). Thus if both PHP 5.3 and 5.4 are installed, you could only select one to run via DSO, the other would use a different handler.