Yes, you can use AMS when you are also on other retailers. To target readers on other outlets, I'd suggest trying out Bookbub click ads too. You can buy David Gaughran's Bookbub guidebook before attempting them. It's great and helped me to finally construct ads that brought in a decent ROI. For a year or more I was struggling to get my ads to work but his book gives great tips and techniques. There are also Facebook ads but those never worked for me.