Hi reikibill ,
Welcome to Adobe Forums.
You can use the Creative Cloud on the third machine but in order to do so , you need to deactivate Creative Cloud from any one machine because as its mentioned above a subscription can be used on two machines only .
In order to deactivate you can use the below mentioned steps-
1) Launch any product from Creative Cloud Application.
2) Click on 'Help' Option.
3) You will get the Option to 'Deactivate or Log out ', click on any one which you see and it will be Deactivated from one machine .
In order to use it on more than one machines you can also refer to Team Membership , below is the link you can follow to know about Team Membership .
Let us know if that helps!