I've had the KCI Firefly and Soundbolt's in my system for several months. The Firefly ICs have been in my system the longest, probably 4 months. I started with the Firefly's and have been slowly adding KCI cables as money and time allows. Both the Firefly's and Soundbolts have Eichmann silver bullet terminations.
For reference here is my system (going through changes):
Blueray Sony BDP-300
Cable/Satellite SA8300 HD (HD DVR)
Video Display/TV Pioneer 5080HD Plasma
Digital Source PS Audio Digital Link III Cullen lvl 4 moded (DAC), Sony CDP C77ES (5disc changer)
Preamp Odyssey Candela
Power Amps Odyssey Kismet+ monos (Stratos Case - Fronts), Odyssey HT3 (Center and Surrounds)
Speakers Kef Reference 205/2's, KEF Ci200.3QR (surrounds)
Speaker Cables Auditioning KCI Firefly's (normally Groneberg Ref tri-wire)
Interconnects KCI Firefly DAC to pre, KCI Pegasus (Digital Coax), KCI Soundbolt monos to pre, BJC (Toslink/HDMI), Groneberg Ref
Power Cables VHAudio Flavor 4 (amps), VHAudio Flavor 1 (DAC), LessLoss (pre), Groneberg Reference
Racking JSP Bolero Credenza (espresso)
Power Con PS Audio Quintet
Previous cables tried: Groneberg Reference, MAC Palladium, BJC, Monster
Music: Dadgum nearly everything I have - female vocals, Blues, Jazz, Country, Classical, Opera, Reggae, Rock, Metal (good and bad recordings)
A lot has been said about the Silkworms, Firefly's and Soundbolt's. I've never tried the Silkworm, but I've found a synergy with the KCI cables...
Most have mentioned how the Firefly's are fast and detailed; the bass is tight and defined - agreed. I'll also agree that the Firefly's are not forgiving, but extremely neutral. They have detail, lack warmth, but are not sibilant or screechy.
The Firefly works wonders with tubes, it provides detail in the highs with the added warmth of tubes. I've tried the Firefly's both from source (DAC) to pre and also amp to pre; I didn't like this cable from amp to pre (too much detail), but from source to pre it is a killer! I'll have to say when used in the right location they add tremendously to the overall listening experience.
The Soundbolt's are at the bottom of the KCI line, but they are not at the bottom of the listening tree. I've also tried these in several locations; source to pre and amp to pre (where they are now). When using the Soundbolt's from DAC to pre I felt they were an excellent cable, but with the warmth of the tube pre I felt I was missing something. When moved - amp to pre, they really shined. Increased bass impact, quiet background, nice detail. If you have a SS pre this would be an incredible cable source to pre!
Now for the synergy part... a Firefly from source to pre and add the Soundbolt from amp to pre (system dependent). You have the detail of silver in the Firefly from the source and the warmth of copper from the amp and viola it all comes together. Now if you add the sultry sound of gold in the Pegasus as your digital cable of choice it is an amazing combination!
Obviously I'm not a professional at reviewing and this is extremely subjective, but I think the KCI cables are a tremendous value and only add to the enjoyment of your system. Definitely give the Firefly and Soundbolt a try.
PS: I know John doesn't advertise it on his website, but he also makes speaker cables and I've been auditioning his Firefly SC for a while. This is too long already, but needless to say it's as good as his ICs! I'll have a set of tri-wired KCI SC's as soon as finances allow.