Likely the Kaisertone music app on the 5S is set to upsample and not sending a bit perfect signal to the Dave. The same app on the iPhone 6S is not upsampling before it sends the signal out. Try to see if there is a setting difference between the 5S and the 6S in the app. The Sony simply does not play DSD natively over USB and converts to 176.4 PCM (actually, I think the Sony converts DSD to PCM internally as well). If you aren't getting the expected sampling rate displayed then the issue is from the source as the Dave just shows what it's receiving.