I wouldn't waste money on overpriced cables, I guess that's just my opinion. Tried em and can't say there's a difference, and electrically there shouldn't really be much audible difference after proper gauge and shielding are addressed.

As far as CD players go, I'd say after $500 it diminishes quickly. Amps vary depending on the speakers you intend to drive, but for all the speakers I've heard it definitely starts to drop off in the $4000-6000 a pair range.