Assuming the room is on the smaller side, my guess is that you would be fine. I've heard of the Diavolo driving similar efficiency speakers with no problems. As Ingvar stated, the Almarro 205 MkII, with a mighty 5 watts / channel, kept up just fine.
Right now, the Kotaros are in my home office connected to the Primaluna Prologue 2 @ 40 watts /channel. With the volume at between 8 and 9 o'clock, things are plenty loud. The Kotaros really love tubes and the PP2 sounds wonderful.
That said, with the PP2 heading into my new work office, the plan was to go with an Almarro 318B - a fine amp indeed. However, things changed when, after talking with a few people familiar with the Kotaro, it was suggested that I consider going with one of the Triode Corp amps. After a little bit of reasearch and talking with the head of Triode himself, he assured me that pairing their 300B monoblock, a parallel SET running 20 watt / channel, would be more than sufficient to drive the Kotaro and that they sound wonderful together as well.
Afer about 40 hours of play, these little guys have really opened up and sound magical and, in my opinion, are worth every penny.
BTW, you are one lucky guy - the Diavolo is absolutely stunning!