Do you know if your Flac file is 16 bit/44 kHz? There's a new HD-FLAC that I download 24bit/96 kHz. Any chance you have those or ALAC files to test?
Interesting that the new MKX offers the audiophile's REVEL system yet old sync with no capability of listening to true lossless format...what's up with that? Makes no sense as Sirius quality is a joke and I really don't know anyone that listens to CDs anymore. How would you truly take advantage of this pricey system. A high end system would only highlight the lossy format... Bluetooth also has limitations in quality too, the USB drive through sync would be the only way to listen to HQ.