Hopefully there is a solution for it. anyway... my car factory head unit has pretty good sound quality so when I installed CarPC I did not go for a aftermarket amp and I decided to use the factory one. I opened the unit and I could locate the preamp chip and the actual amp ICs that are connected to the big heatsinks behind the stereo unit, then I soldered wires to the amp chip inputs and I could have an amp without purchasing a aftermarket one.
it is serving me for over a year now without any problems... sound quality is awesome... BUT since the first day (1 year back), when I started to use this, I had problem with choosing the right USB sound card.

when I plug my 10bux Chinese MP3 player into it, sound is perfect, but when I plug my 500bux iPhone into it, sound volume is really low, whereas iPhone volume is in the highest position!!! and when music bass starts hitting, car speakers start popping like they can not handle the sound but I hardly can hear the actual music!!!
I have tried more than 10 different USB sound cards ranging from 2 dollars to 50dollars from eBay and all ended up with same result :-( but finally I purchased a brand new Chinese USB sound card for 20bux shipped, and it amazingly worked!!! and is working for 1 year now.... sound is amazingly perfect... couldn't be better than this :-)

this is the Picture of it...


BUT it cuts off the sound in really hot summer days and I have to restart the CarPC... so I decided to go for another sound car.

I was really interested about Creative Xmod sound cards since I started my CarPC but I never had enough cash to purchase it.... and finally I purchased it last week... but I have the same problem as before even with Creative Xmod USB sound card....

Does anyone know why it is? why expensive products wont work with my car factory amp but cheap Chinese stuff would?