Distortion with FLAC only, DAC+ Pro and Volumio

Hello all, I'm running into a strange issue using a Dac+ Pro with Volumio.  The setup works perfectly and sounds flawless with all sound files I've tried except for 24/96 FLAC.  The FLACs have a layer of mild distortion in the mids and highs.  This does not seem to be affected by the mixer settings.  The version of Volumio is 2.224 on a R Pi 2.  The files are being played directly off of a USB flash drive.

If I enable Audio Resampling at 24 bits/48kHz in the Volumio settings, the distortion with FLAC goes away.  If the Sample Rate is increased to 88.2kHz, the distortion returns.  The distortion remains but is lowered when the Sample Rate is set to 96kHz.  The file will not play at all if the Sample Rate in increased beyond 96kHz.  If Resampling is disabled, the FLAC distortion comes back.

If I plug in a USB DAC and disable the DAC+ Pro, and set up USB as the sound output with no other changes, the USB audio does not have the distortion with FLACs.

Any suggestions?  It's probably just a setting.  And it may indeed be Volumio; these FLACs are 24/96, but Volumio states in the UI that the files are being played at 24/88.2.  Thanks for all the help in advance.

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