If you are on Windows Vista/7/8, I guess that you just have to enable the "listen to this" option. (Right mouse button on speaker taskbar icon, Recording devices, right mouse button on microphone, properties, Listen tab, listen to this device).This might not work with all soundcards, but then, you might have an option in its own settings dialog.
Since this is being claimed for the deviceM-Track offers ultra-low latency monitoring of the input signal -- either through the speakers or via headphones. The monitor mix knob adjusts the balance between the direct inputs and the playback from your computer software.It says that you can mix the vocal input with the computer tracks playback and send the mix wherever you want via the monitor connections.The computer playback must be sent to the device via the device settings of the program you are using to play the tracks. The device monitor mix must be used to mix the two signals to your liking. As long as you can achieve playback from the computer, you should not need to care about any other Windows settings.If you also want to record your vocals, as you wrote, you must use a recording program that allows recording and playback at the same time.,Some do, some don't. This part will require the proper Window settings for recording.If your recording application provides for monitor playback of the mix, existing tracks plus new input, then that mix can be sent to you speakers or headphones via the device output, keeping the MAudio device monitor mix set to zero. This probably will mean greater latency between your vocal input and what you hear from the speakers. You have to find out if it is enough to be a problem.
It is perhaps the most common thing to do with any professional recording setup. There may be some sound cards (not gaming/entertainment audio cards) that cannot, but I don't know of any in particular.
Not according to the Thomann sales chart. They listRME, Focusrite, Native Instruments, Steinberg and Berhinger as the top sellers. More experience and better bundled software probably.