There are two things to consider here. Low-impedance, high-power lines suffer more from power loss through long lines. High-impedance, low-power lines are more vulnerable to noise when they are made long. So those are the vulnerabilities you'll have when either is made longer.

Fortunately, with the distances involved in home audio systems, neither is usually a problem. You can find an easy solution either way you do it. If you make the speaker wires long, make sure they are large. And if you make the preamp level lines long, make sure they are shielded and not run near electrically noisy devices like florescent lamps and large appliances with high current switching relays or commutated electric motors.

Wayne