Reducing a line signal in the home HiFi system
If the connection already works (just too loud) there isn't enough DC component to worry about.

The only things it might do to damage fidelity are both minor:


The resistors act as an additional noise source: with the CD paused and the volume fully up you might hear a slight increase in the faint background hiss : by all means test that, but I doubt it. (Return the volume to normal afterwards!)
Slight reduction in high frequency response. As you are putting it in the CD player, the two resistors in parallel (call it 15k) and the cable connecting it to the amp (probably below 1000pf) will roll off the high end slightly. 


For C=1000pf, RC = 15us, f=1/(2*pi*RC)=10kHz.

So if the cable (and any input capacitance in the amplifier) came to 1nf, response would be -3dB at 10kHz. This is worth fixing. 


You can choose a low capacitance cable and impress your friends hey, cables really DO sound different!!!
You can build the attenuator between socket and plug, and wire it after the cable (so the cable is ahead of the attenuator)
you can reduce both resistors by a factor of 5-10. Say, 6k8 and 5k6, -3dB at 50kHz, -1dB at 25kHz, probably a reasonable compromise
you could build the attenuator into the amplifier instead.