Best possible digital output from a computer?

I've recently purchased a Yulong DAH1 Mark DAC (Chinese brand, not extremely popular). I have to say that so far I am pleased with the sound, and have been using the USB input which is fed by my personal laptop running Foobar or Media Monkey. However, I'm sure that this is not the best possible route, being that this DAC uses the PCM270x chip to accept the I2S stream via USB, which adds another thing into the signal path before sending it to the main AD1955 DAC chip. I believe the sound would be better through coax or optical, but what would be the best way to get a coax/optical output on my laptop? It has neither of those outputs built-in....

Thanks in advance.
Yes, that is certainly the case with the SPOILER. As for the USB cable, I'm using a 4 meter Monster with very good effect.

I'm sorry, could you please clarify as to what is the case with the SPOILER? Do you mean that the USB output sounds the best out of all the available outputs?

I'm trying to determine why the soundstage depth is so poor with this unit. It could just be a design flaw, but there may be something else to blame, such as the quality of the USB cable, or the setup of my computer.

The coax output in this DAC may be better than USB, but I have no optical or coax output on any of my computers to try this. It seems as though getting a USB to coax converter for the PC may be the only way to go.
I've been doing a USB to coax conversion with an ESI U24 soundcard (no longer available, but a very good unit). However, my results are mediocre at best. There are so many issues though from the initial ripping, format, PC, USB to coax, and digital cable to D/A. I can compare the original CD to the ripped version and the original CD is winning by a pretty wide margin. This should not be the case from what most people tell me that really know digital (I am definitely NOT an expert in this area).
Bel Canto has just announced the Bel Canto USB Link 24/96,
a USB-to-S/PDIF converter which looks interesting. Will be unveiled at CES.

My Toshiba has, like your laptop, except for firewire, only USB output possibilities. I have no complaints about the soundstage, which is both wide and deep and I see no deterioration at all with the Spoiler compared to vinyl or CD direct. So I tend to doubt that USB per se is your culprit.