When the Gemini first came out, it had mono speakers - not through design. They were loud, but tinny. I thought the cosmo would be similar, however I did a few tests today, and was very pleasantly surprissed. The speakers are most definitely stereo, they are loud, and less tinny than gemini. I still wouldn't put them in the same boat as say a good bluetooth speaker, but they are quite usable. Stereo separation is excellent, and there is plenty of volume to play with.
I played oxygene at full volume and was actually amazed at the quality and quantity of sound eminating from the little beast. I haven't installed an equaliser yet, but I would guess you could sacrifice a bit of volume for better sound. I would be interested in hearing what other people think of the sound. There are some good audiophile sound tracks on youtube, but if you have a decent bitrate mp3, I would think that would be better.