The C1 IIs sound better than the Mk Is, but I would take that Diablo bargain from your dealer in two seconds flat!
By the way, I used a Storm III for many years with several speakers, including B&W Matrix 805s, 805s and 804s. One thing most people don't know about RELs is that they can improve the bass of almost any speaker, but that's not their main advantage; it is the way they improve the soundstage and the general sound of the main speakers because of the ambient clues hidden in the low frequencies and the way they 'come from underneath' the main speakers.
Enjoy the music!
By the way, I used a Storm III for many years with several speakers, including B&W Matrix 805s, 805s and 804s. One thing most people don't know about RELs is that they can improve the bass of almost any speaker, but that's not their main advantage; it is the way they improve the soundstage and the general sound of the main speakers because of the ambient clues hidden in the low frequencies and the way they 'come from underneath' the main speakers.
Enjoy the music!