Thanks for your input Arindelle. I will certainly check out your input. Meanwhile I have done some other things and it seems I have found a stable set up now. My analysis and conclusion is that encoding all files to DSD over DoP ("output encoding" in DSP Studio) is not fully stable in my set up (ADM A6-4400 M APU/8 GB -> WD Elements HD 2TB -> Windows 8.1 -> WASAPI Ext mode -> Aesthetix Romulus Signature SE dac/cd-drive). So now I did the following:
• Play files from memory (Audio -> settings)
• Pre-buffering 100 ms (Audio -> Device settings). I started with 500 ms, then 250 ms and now 100 which still works. 500 ms was actually too much which gave some abrubt ends of each track.
• Output encoding none (DSP Studio). Before I encoded all files into DSD. I think this was the main issue.
• Sample rates output -> no change (DSP Studio)
• Bitstream DSD enabled (Audio -> settings)
The result of last three settings was new to me. It means that original format will be sent to my dac. The display now shows, 44,1, 88,2, 96 .... or DSD, i.e. the original format of the file. When using output encoding DSD in DoP all PCM-files are converted to DSD.
What did what of each new settings can be discussed. Important for me is that it now works and it plays beautiful. I'm very pleased.