Can I use other payment gateways with DMXReady products?
Yes. You have full access to your source files so you can "custom add" other 3rd party payment, shopping cart and checkout options/buttons. Simply open the files using your html editor and copy/paste your 3rd party code.
Learn how to add google checkout: http://code.google.com/apis/checkout/developer/Google_Checkout_Basic_HTML_Overview.html