I've checked the forum and I know that M-CR603 is not "officially" listed as spotify connect compatible.
Nonetheless, it works fine with :
- my mac (through the system but not through the spotify app)
- an iPhone (through the spotify app)
But it doesn't with my Android phone.
I guess the device is not fully compatible, but I was wondering if it may just be due to some settings or minor developments in the spotify android app ? :)