How is online radio so transparent?

I listen to Radio International Jazz streaming on the internet at my office. I have a Philips Mini system for this. It's a very good sounding mini system but is truly lo fi. It's connected via rca to mini plugs to my Dell desktop. In this very cheap setup the speakers play with extreme transparency, midrange detail and clarity, midbass too. This little system really cooks. To my ears this kind of performance is right up there in the upper mid-fi. How is this kind of quality possible with these electronics and speakers?