Musical Fidelity X10-D "The Missing Link"   Pure Class A triode (valve)  CD line stage (buffer) Improves the performance of any CD player which is connected.

All you have to do is take the analogue output of your CD player and connect to the input of the X10-D then take the output of this unit and connect this to the CD input of your amplifier.

Below is a review from a forum site.

I have been into Hi-Fi for years moving from great analogue systems to poor CD sounding systems with all ther clarity but metalic sound. My current system is a Musical Fidelity CD1 palyer, Musical Fidelity A100 class A amplifier, Musical Fidelity MC2 speakers (Bi wired) and a Sony 100 active sub. The overall sound was detailed but glassy and I was looking for that elusive analogue sound without the narrow range and detailed and without noise. So far an expensive 10 year experience. Looking in Hi-Fi mags I was interested in a valve option to change the sound. I brought a X10-D on Ebay with the hope it would turn my Hi-Fi into my dreams. When I connected it between the CD and amplifier I expected to hear a subtle difference. I was blown away, the change in sound was astonishing. The detail remained but the vocals were beautiful and the sound stage improved beyond dreams. Listening to Katie Melua, like I am at this moment the vocal is so sexy and the air around the stringed bass is fantastic. This is like being in a smoky night club and she is on stage in front of you. This is the sound I have been looking for, it is beautiful. It works the same for classical and rock. At this moment I am listening to 'Ten Million Bicycles' and it is so real she is in the room with me. I will never part with this device. Buy one and you will never know how you listened without it. Half way up the Hindu Kush is now on and it is the best HiFi I have listened to!

Strengths:
Changes the musical experience from digital to beautiful. The most simple but most musical upgrade you could ever buy.

Weaknesses:
No way of turning it off.

NB:  Selling this unit for my friend so have no idea as to how much the sound will improve. Also there is no buy it now.