I donít know about the other two but I have heard the Cmoy but only used with headphones. Sounded fairly good. From what I understand the normal gain (boost) is set to a maximum of 11. That should be just about right for an AUX input. However the gain can be changed by simply changing a resistor. If you do get one ask and make sure that the gain is set to around 10. IIRC the one I listened to was set to a gain of about 4. Thatís fine for some headphones but not for an AUX input.
If what you are listening to has a headphone output (not things like a GPS or other SAT receivers) check out this post.
It wonít drive headphones but doesnít require batteries.