fireball106

I have a Pioneer DEH-P880PRS head unit in my car, which is connected to 2 amplifiers (front stereo, sub monoblock).

I would like to buy a laptop with a dedicated sound card, and connect it to car.

I encountered the Car2PC adapter for Pioneer which connects to the PC using 2 RCA cables and a USB cable.

I have several questions:

1. What sound quality can I expect from the Car2PC adapter (I have a pretty good and revealing SQ setup in my car).
FYI: It uses the LPC2100 Analog-to-Digital converter. Here is the electric diagram for the Alpine model.

2. Why is this Digital (PC) -> Analog (Sound Card Output) -> Digital (Pioneer AUX input) -> Analog (Pioneer internal DAC) conversion needed?
How come no-one created a product similar to Car2PC which has a DIGITAL input? That would improve Sound Quality.

3. Is it possible to connect my sound card AND the head unit to the amplifiers, in parallel? Do you think it would result in better or lesser quality.

4. What sound card do you think I should choose? I heard the EMU 0404 USB is really good in terms of SQ. What about Echo Audiofire 2/4? Dmitry from IndashPC said the Car2PC adapter audio input should receive a maximum voltage of 1v.

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Lior "Fireball"

MP3Car.com