very good question I'd be worried about the bass response.
Also, I researched these RAAL ribbons quite a bit, and heard a couple projects with them. They are very nice sounding, but personally I preferred the Raidho units. I think the RAAL ribbons are really meant to be driven by tube gear (see their marketing stuff, they were almost designed this way) and that wasn't a limitation I was willing to accept at this price range...