Unless you have some long wire runs, 14ga wire is more than enough for almost any speaker out there. Even in large home theater systems with in-wall wiring, the largest gauge wire is usually just 12ga.
Luckily your system doesn't use very large amounts of power. The receiver is rated for 20 WPC at 4 ohms and the speakers are 5 ohms nominal impedance. The wire gauge that came with your unit is probably more than enough, but you can always spend a little more on good quality cable (like Belden) with good quality connectors.
