Importance of computer for DAC shootout


I am using a perfectwave DAC + bridge + modwright 36.5 LS/PS preamp to stream flacs over my network. Very happy with the sound, but intrigued by the idea of getting better SQ for less $$$ I will soon be auditioning an Antelope Zodiac Gold + Volticus over USB, directly into my poweramp. Being able to take out the modwright alone would pay for the new DAC. My only concern is the Computer I will be using for this shootout. I have a Dell laptop and an Asus media PC, both with USB 1.0.

If I opt for the Zodiac I will go all out on computer source (may be mach2music), but I don't want to invest before knowing if I even want to go down the USB path.

In you estimation, is there any chance of the computer used in my shootout distorting the outcome? Would I be better off using my Marantz ud9004 S/PDIF source for the Zodiac, and then get a better computer if the Zodiac wins the contest?

Or are the difference between computer sources small and will I be able to conclude which is the better DAC using a mediocre PC as the source for the Zodiac. Any advise on how to set up the hardware for the shootout is welcome.
edorr
There are so many conflicting opinions and observations about what it takes to turn bits into a good analog signal I have no clue what advise to go by. You can spend over $3K on the latest mach2music with external powersupply and audiophile USB cable, while your DAC manufacturer will tell you your asynchronous USB DAC is pretty much immune to the source anyway. You can spend 10K on a tube preamp and your DAC manufacturer will tell you taking it out of the chain will improve SQ. So I only go by personal observations in my own system - I have no experience with USB DACs but in my experience DACs in general make a huge difference (transports not so much). Just want to give the Zodiac Gold a whirl, simply because it gets good press and it would pay for itself if I can take out my preamp. If it does not deliver the goods it is up for sale in A'gon. How far I need to go optimizing my digital source is still a shot in the dark for me, notwithstanding all the advise I have been getting. I'll probably get a mini mac to be safe and upgrade to mach2music if I decide to go the USB route.
i'm not a usb fan but won't open that can of worms in your thread. i recently compared a macbook pro to my win7 pc and found no difference what so ever (streaming with both). not sure if the mini has any advantages over the macbook so i can't comment on that. do agree with others that using an old pc is not a good idea.

comparing file types, i found flac and wav superior to aiff and alac. wav and flac were identical to my ears.
I just got the Mac Mini at a price I can resell it for in a heartbeat so no exposure there. I will be using pure music with Flac's.
As important would be to make sure the computer is on
a different power circuit to the rest of the hifi. Keep it isolated so
you don't add noise.
I am using 2 PS audio P5 regenerators, which provide isolation. I would assume this should be OK.