Just some notes:
Coax is shielded to prevent interference.
CAT5 can be shielded and is inheritly protected from outside signal noise due to its twists. Although, must of that "noise" comes from other pairs in the same CAT5 cable, thus each pair is twisted differently inside the CAT5 cable itself.
Speaker signal wire is potentially your most "powerful" set of wires running in your bundle. You won't see much interference coming into the speaker signal from the other two sources, and those other sources are designed to block signals from leaking in/out.
Long story short, you are fine unless doing really long cable/wire runs.
Now, just remember, a coil of copper wire with electricity running through it is an electro-magnet. Not a strong enough one to worry about though. Just sayin'...
