I have time now to test some audio equipment combinations. I try to find a ”low-end” solution (low price and great sound quality) Found this USB-only VARNA DAC (http://www.alldacinfo.com/?p=9392 from Ivelin Yovchev. Working everyday now with this DAC is still a great pleasure. Low price with a exellent sound quality.
I tried to get more out of the DAC to use a modified laptop Lenovo Thinkpad X200 (OS Windows 7 enterprise) I stripped all unnecessary services, programs, memory options, etc.) The results are great, much better as I expected. A small fanless computer, dedicated for audio only will maybe a much better solution.
I found the Linux Volumio project on the internet and decided to give it a try. I ordered the Raspberry Pi small computer. I am not a Linux guy but with help from the very nice and instructive Volumio website I installed the Volumio linux OS. No problems at all. The DAC was working directly without any driver problems.
The sound quality is very good. A little less than my laptop solution. But when you look at the total price, the price performance for the Volumio is much better.
With this little test I found out, that the combination computer (components) + OS (Windows , Linux) is a very important aspect of your total sound quality.