The First Watt amps are lower powered but for a tweeter it would be fine, and I think the FW5 is up their most powerful.
Another option for the highs, and my favorite Nelson amp is the Aleph J, released in about '04. It is popular by horn lovers because of the very low distortion that horns can magnify. It is essentially an Aleph 3, in a Aleph 30 chassis, w/ a low distortion J-FET front end. It has a tube like sound and 60wpc. They show up on Audiogon from time to time. It is the very best of the Alephs (according to Nelson) and should make your tweeters sing while blending w/ your Aleph 2s for the lows.