Improve sound

@erik_squires 

Those aren't ESL's it's their box speaker with the AMT tweeter.

https://www.martinlogan.com/en/product/motion-40i

Thanks @sunshdw for correcting me.  Sorry, my bad!! :)  AMT's have great electrical performance so ignore me!!! I SAID IGNORE ME!!!!! :D

So that leaves the room.....

I like the Martin Logans. I think a tube DAC might give them real warm and liquid sound. MHDT Orchid comes to mind.

Although your speakers have a fairly high sensitivity specification, they are a 4 ohm impedance load. Your amp does not provide a spec into a 4 ohm load. My guess is an amp is needed that likes a 4 ohm load or find a speaker with 8 ohm impedance. 

+1 to the Orchid DAC or a Denafrips  or Pure Audio. The SQ of the Cambridge is OK but the app is rubbish.