How does upsampling affect cd playback?

I was listening to the Music Hall Maverick SACD player the other day and discovered something that was startling. When playing a redbook cd, you can swith the sampling rates on the fly and there is a noticeable difference. With this particular disc, the soundstage seemed to move forward and there was more spaciousness to the sound. My question is why? How would sampling rates make a difference?

Thanks for your input.