I've used the 2226h in 3.5 cubic ft box with SETs from 1 watt to 18 watts with good results. However a 55 watt 6550 P-P is incredable!!! My complaint with the 2226hs is the midrange more than bass. They have very smooth flat midrange but a little dull sounding at low levels. It takes a few watts to liven them up.
I would recomend a 15 watt P-P 6B4G as the starting point. If you can't play music that loud consider a livelier speaker. The PI 2s look good also Hammer dynamics get good press.