The USB to SPDIF box need not be an arm and a leg. There was a brilliant small device called the Waveterminal U24 which helped launch this whole evolution a few years ago. Trick is that it got its power from the USB cable which carries 5v - ergo no costly power supply, no big case etc.
Then Hagerman came out with one.
The hot ticket now for under $200 is the BlueCircle USB Thingee.
All these devices take the data from the USB and move it over to SPDIF. Neat, simple and compact. I can tell you from experience that I found that it took a very good SPDIF cable to make this work its best.
I do not believe that USB implementation is all that difficult. What I believe is that most audio manufacturers have their head in the sand hoping that the whole computer thing will go away.
That is why companies like Keces (and there are many others, just my current fave) who have a global perspective on the mass market are investing in figuring it out and evolving it.
What is wrong with this picture? USB/SPDIF conversion box $500, SPDIF cable $500, DAC $2500, allowance for power cords and tweaks $750... You don't need to spend $4,200 to get great sound from a $100 hard drive and some free software... think about it.