Hi Jewel, Coincident has a new speaker called the Victory that is 97db 14-ohm that should work great with the Graaf. I have not heard this speaker but I own the Coincident Totals which are 3db less efficient than the Victory. I get very good results with a 12 watt amp so I would think that your 20 watts would should be more than sufficient.
Good hunting.
Good hunting.