richard...definitely consider Audience Au24 cables for your I-5/FS688 combo. I'm a Focus Audio dealer (and a big Sim Audio fan) and have found that the Au24's mid/high frequency performance is an excellent match for the FS688. Also, if you don't plan on bi-wiring, make sure you upgrade the jumpers that come with the FS688.
(disclaimer: I am an Audience dealer, too)
(disclaimer: I am an Audience dealer, too)