I am pretty sure they are D4S like you said. Somewhere on this forum it is confirmed exactly what they are, but I couldn't find the post.
The only google result I found was
http://www.tdcautomotive.com/Subaru-...et_A1841A.aspx
It does seem to confirm your question though. I have been meaning to get some new bulbs too, are you looking at a specific type?