Harleyduo,
I have not been to the smart house, but I believe I can answer this question for you. The standard stereo unit on the Passion Coupe is a single CD player (model Radio 9). A premium unit with the 6 CD player (model radio 10) is optional, and standard on the Passion Cabrio.
The Canadian smart brochure illustrates both units quite will. The radio 10 unit has a single slot on the front to accept the CDs (which presumably are then stacked internally). Note the standard equipment on the Canadian and US smarts are slightly different (Canadian Passions all get the radio 10 as standard).
http://www.mercedes-benz.ca/mbccusto...ochure_eng.pdf
(radio 9 is on page 29, radio 10 on page 33)