There was a harshness to the sound, especially in the high frequencies. I think the best way to describe it is an inconsistency with the notes. I believe that it is caused when jitter occurs with the digital stream going to the DAC. The bits are not timed well and this can be very audible with a good system setup. If it is slightly off listening fatigue can occur. Even the best DACs can be susceptible to jitter. My Lavry DA10 claimed to reduce jitter, but I still could hear it. My Cary 306/200s have very good DACs, but they also do not reclock the incoming bit stream to totally remove the issues.
I spent a lot of time trying different settings and different audio cards. The RME cards that I am currently using are used in the recording industry along with my Card Deluxe and the Lynx which I do not yet own. Trying other cards I have found that digital sources do not all sound equal. The professional cards have more hardware and rely on Windows less to get the bits out in a timely manner thus reducing jitter.
Does version 13 have a dedicated thread to getting the audio out? I hope the UI and the new features that have been added are not effecting the audio processing thread. Hopefully the UI threads are running at a lower priority than the audio processing.