Hi All,
I sent this to Drummer earlier in a PM.
Hi Don,
It’s an interesting question. Most people assume that the tweeter is a very low powered driver so not much power is required. Also most assume that a lowered powered amplifier having a less complicated output stage will sound more refined.
On the stacked PMC Active systems (BB5's, MB2's) for instance we use a 4B on the tweeters instead of a 3B because the highs just sound better. It is to some degree system dependent so there is no exact answer.
I have found the 28B’s sound really sweet on the tweeters but it does seem like overkill on just a tweeter. As a matter of fact we have a standing joke around here that the 28B is the best tweeter amp we know of.

Some customers have used a 7B on the bass and a 28B on the mid/tweeter with good results.
James