I've gotta chime in here one more time to say that I've tried out alot of caps for high frequency tasks like single component tweeter crossovers with some super high end Fostex drivers (FE208ES-R and T90A-EX). I eventually abandoned the tweeters, BSC, or, really, any treble adjustment because I couldn't find a cap, resistor, l-pad, etc. that sounded "right" for the tweeter.
That is, until I heard The Fix with the Orcas. The sound of those polystyrene caps doing their job at the line level was so effortless and transparent that I just don't see a way of getting a tweeter to work out as well unless it was way higher end than even the T90A-EX or something. Paper cone highs can sound really natural and smooth, but are always locked in exactly the same proportion with the rest of the fullrange driver and/or often become directional the larger you go in cone diameter. Metal tweeters just tend to sound, well, metallic to me no matter what, and ribbons are nice, clean and sound really "deep" to me in a good way, but seem to outpace most of the direct radiator woofers that they are mated to. Overall, there are so many compromises out there. I could go on and on, but suffice it to say that I think it is really tough to "tweet."
The Fix is a really compelling tweak for me as an FR guy because I can just get more highs from my favorite driver if I needed to. For that matter, its great for anyone who needs a different frequency response from any old speaker, Orcas or otherwise. For instance, for speakers with the "bad sounding" kind of speaker level HF and LF boosts, you could zero those out, and use The Fix instead... Lots of possibilities. I really wish I had The Fix back when I was listening to Fostex 6" ers - Fantastic drivers in many respects but rolled off in the highs to my ears.
Cheers!
-Clark
