I get lots of visitors to my place listening to my humble setup and one of the most fun trick I play on them, is to let them hear out this little tweak. The look on their faces and the realization that it's so easy to do this tweak is... priceless.
First thing first, does your CD player has a digital output? If it does, then chances are this tweak will work. If it doesn't, then you are missing out all the fun!
Solder a 75 ohm resistor between the signal and ground shield of a RCA male plug. I'm assuming your digital output is RCA here. This resistor can be the tiny 1/8W. Bigger doesn't matter. If you have difficulties finding 75 ohm, then just parallel 2 pieces of 150 ohm. Oh yeah, no need for WBT or audiophile approved resistors here. Try it cheap, for once.
This is it!
Now, impress yourself by doing simple A-B test.
A: with plug plugged into digital output. listen.
B: plug removed. listen.
Then A-B-A-B, get spouse to A-B-A-B, get audiophile best friend to A-B-A-B...
If you hear a difference, then congrats! This tweak works for you! If you don't hear a difference, then probably the manufacturer has taken care of this problem. What problem?!
You see, electromagnetic theory says that at high frequencies (can't remember what frequencies), signals don't behave like they normally do. Electrons get...delinquent. If a low frequency signal reaches an open circuit, nothing happens but if a high frequency signal reaches an open circuit, it BOUNCES back! This is called signal reflection and is the basis of that instrument (can't remember what it's called) used by TNB to locate where the underground cable fault is. I mean, you know there's a fault somewhere, but WHERE? With this instrument (can't remember what it's called), TNB engineers can trace it down to the +/-50m (or something like that), and the rest is up to experience!
While this principle of signal bouncing prevents TNB guys from digging EVERYWHERE trying to locate a fault, it helps us if you could reduce this bouncing. Better still, eliminate it and the best way to do so (this I remember!) is to terminate the line impedance with the equivalent impedance. Since we are using 75 ohm line, then 75 ohm will do. With no more signal reflection, you have improved your source signal! Prepare for better defined images and lower noise floor.
If some engineer bark at this, saying the frequency of the digital signal shouldn't matter, never mind. Trust your ears.