Upgrade speakers or DAC

I used to say speakers but, the source is where everything starts and stops

if the signal is not very good from the start you can’t make it up down stream.

Big jump from Cambridge to dCS DAC, I would assume. Do that first and speakers afterwards. 

Speakers!

Speakers will always make the biggest different in sound quality, bar none.  The question is when does one stop ?

Always source you will be amazed that when you have a great source how much better your system will sound. The speakers can only produce what is feed to them.  We have used old box speakers KLH form the 70s and found that they disappear with a better source much to our surprise.