I found that the AK120 is quite good for W1000X as well. The somewhat unique feature of the W1000X is the tube like signature that it got, which is very nice but after a while get a bit too much. The AK120 is able to calm the headphones down to a managable level and tune the colouration back a bit, which is more or less the same effect it has with the CKW1000ANV.
So far I am very impressed with the way the AK120 is able to drive low impedence headphones such as the ATH-W10VTG, ATH-W1000x and ATH-W100. The only headphones that I don't really like with it is the ATH-ESW11LTD, which I perfer to be driven with Z-1070 and P51.