I know this has been discussed in various other threads but i can't seem to find a definite answer.

I building a car pc using a laptop so will need a USB soundcard/dac

I have a 4 channel pioneer amp with outputting 4 speakers
I want to be able to control front/rear balance and right left balance separately (as you would do in with a normal head unit)
With a normal stereo out and splitter this can't be done so I need a 5.1 (or a 4.1) soundcard

So far
1. Creative X-FI (?built in dac) - mixed reviews. Issues about CPU load,loud thumps etc but does have 5.1 output which I presume i can use to get separate outputs so that centrafuse or some other mixer programme can control the different channels.
2 USB DAC- i have only been able to find 2 channel DACS. not sure if there are any 4.1/5.1 USB dacs out there

I want all my mp3 and sounds being played out of 4 speakers.
So my question is a. What product is best used (i.e quality and ability to control each channel)

Are there any other USB 5.1 soundcards? Or 5.1 USB dacs.
Will I need additional programmes to implement this or will centrafuse let me control 4 channels.