In windows, in the lower right hand corner (system tray). Is there a little speaker there? which when you click on it gives you control over wave, synth, cd, line in, etc.
Just trying to figure out how your soundcard is tied into your system. Like on my laptop, for instance, there is only one windows sound device. I have Samplitude on it and the audio is routed to it. I think it uses a device driver which interacts with the windows kmixer. There is no way to avoid it using that soundcard. Ideally, with an addon soundcard, the driver would allow you to bypass this windows layer and talk directly to the hardware. I think that is called "kernel streaming" in windows terminology.
Can you provide more details? What soundcard? Host OS? Maybe someone has that same setup with experience with Samplitude.