First, I don't think you'll need to pad it 5db. it MIGHT be 1 or 2db more efficient than 105, but even hornloaded I doubt it would give more than 104 or 5 through the useful range.

Anyway, you know more about your driver than I do, so my guess is padding it by 4 or 5db with fixed resistors would actually be better for the amp. This will reduce impedance range(Zmax and Zmin) giving the amp a load that is even closer to being purely resistive.

As for it affecting the tuning of a BR design... I don't know, I wouldn't think so, but I'll let someone else answer that.

hope my guesses are of help, I'm a little bored at work here.

Danny