I've listened to the amp for several 2-3 hour sessions now and really enjoy the way it sounds. The power is adequate for my listening levels 99% of the time and it seems to do well on the Pi Towers.After listening to some Keb Mo for about 30-40 minutes tonight, I quick switched the cables around back to the NAD 320Bee amp and fired up the CD again to the same song I was listening to. First impressions were that the bass was a little tighter (but no lower sounding) and the sound was more flat (maybe neutral is a better description--hell I don't know all these audio adjectives!) for lack of a better word. Sounded fine, but did't have the image and air that the little amp had. I had to turn the volume up on the NAD to achieve anything like the 12B4, so it was basically just louder which didn't accomplish anything. The 12B4 just made it sound like the band was more in the room with me than the NAD. Nice.
Now, according to Akhilesh, his 12B4 amp sounds very good on his K-horns. Maybe I need to start thinking about upgrading to some more efficient Pi's down the road!