I have changed tweeters and mids in my D6K's and would change the 8 bass drivers if my budget allowed.
(The Volt drivers are �135 each)
My friends design speakers and they advised on drivers.
The metal Peerless tweeters had resonances that annoyed, Vifa silk domes were better.
The mid range with phase plug was replaced with a very fast Vifa driver with good dispersion.
They mated very well with the cabs and needed no
tweaks( which are available in the menu).

Interesting things are happening in the speaker world.
The best drivers were designed and built in Scandinavia, now they are increasing built in Asia
some of the best coming from Indonesia !

518, 568.2, D6Ks, D6KC, iMac dual core, iTunes 10.1 (lossless), Apogee Duet, Kuro 500A, Logic Studio, Sound Devices 702.