O/T Recording / mixing advice needed

Hi there,

This is off topic, but this is the only music forum that I go on, and seems to be full of very knowledgeable people, so I hope you don;t mind! here we go:

A friend of mine and I have created a recording using Pro Tools and a digi-design M box. The recording is of a string quarter, plus acoustic guitars, drums, bass and vocals. It sounds absolutely gorgeous on my seperates system, but as soon as we play it in a friend's cheap car stereo (or his cheapy system in the kitchen) it sounds 'thin' and boomy with way too much bass.

We've no idea what to do because it sounds absolutely perfect on my seperates system (and also on the hi-fi in my car). It just seems very sensitive to which equipment it is played on.

How can we make it like a CD you would buy in the shops? i.e. good and playable on any system, but just better on mine. Does this require some serious compression? Maybe the dynamic range of our recording is too great.

help! :-D