Where can I start to improve my sound the most 2ch

Upgrade the CD player.

Room acoustics is very important. It will make more difference than cd players, wire or any ss electronics. Without good acoustics you're not hearing your system as well as it could sound and this is commonly quite an ear opener. For the money it's a bargain compared to what many of us have in our systems. Bass traps can other room treatment can be made rather inexpensively too. I'm sure many of us here would like to hear what you think after you get some room treatment. Fair warning: Once you start and hear how much better your system sounds it's hard to stop.

A separate amp which is on your todo list is also a great idea.
Don't change CD-player now. Many folks believe that your Cambridge definitely isn't Capitole or Burmeister that's why needs to be changed.

1) The room
2) The CDP

The room is the true source of the music, IMO. It will have an affect on the sound that trumps the contribution of the other components. Take care of it first. Then, once you've powered on, the CDP becomes the key member. The amps, cables & speakers can only work with what they are given. Get the best source you can afford.
Just my two cents.

Good luck,
Howard