you shouldnt be using asio multimedia you should be using maudio asio (its a option under audio or midi cant remember off hand ) and your 2496 card is asio 2 compliant which basically means you can direct monitor (ie listen to what you record whilst hearing the
backing track though becareful how you set up your ins and outs or youll record what your listening to including the backings i recomaend finding a book on how to use cubase sx (i prefer vst anyways) also for your test make sure other souncards ie inbuilt ones are DISABLED in control panell and make sure the m audio is set to be main card to sound all the windows sounds and such otherwize the cubase test wont find it if its failing the buffer tests id send the maudio card back or check what buffers your running as i said get hold of a cubase book its explained in depth in them more than i can here