I'm sure this topic is not new. If so, I'd appreciate any AK links. I've ripped a couple of hundred cds to Flac using my office computer and jriver s/w. I copied them onto a 1tb, USB hard drive, play them through my Bluesound Node 2 and sent the digital output, by coax, to the dac in my Marantz Sa8004. Comparing the Flac files to the donor cd, I hear no difference. But, in a demo session, several audio friends claim to hear differences. (Some say the Flac is superior, some the opposite.) I can understand audiophiles who have expensive cd systems being reluctant to accept that a modest, non-mechanical system can equal their high-end systems. But are there any valid reasons for hearing differences?