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I don’t 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. That’s 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.

post

It won’t drive headphones but doesn’t require batteries.

 

OK. You've had some time now. How do you like the Alpine? How about the install? I'm thinking about a HU upgrade myself.