Flac is equal to the raw audio file that was used to create it, it supports up to 8 channels and a incredible variety of bitrate/khz It allows for true bit for bit copy of audio files while consuming half the space.
I use a 250gig hard disk drive plugged into the USB port on my Onkyo TX-NR906 the music sounds incredible, specially my 96/24 rips the clarity is incredible, cds are limited to 44.1/16.
of course a audio file is only as good as its speakers, amp, cables, sub, dac, and reciever.
P.S. The onkyo 906 supports flac natively!