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Jitter in today's electronics operate in hundreds of pico seconds, or one billionth of a second. Some in the audio industry claim it is necessary to stay within single digit pico seconds (one trillionth of a second) to be completely inaudible. Who knows? Pioneer does have a feature on its receivers that link with its TVs and blu ray players called Phase Control which is a PLL circuit designed to reduce jitter. Whether you believe in it or not, some manufacturers have decided to tackle it.
People that claim to hear the difference either have superhuman hearing , have something on the receiver altering the sound besides the DAC or it is the placebo effect.
There is no way a person can tell the difference in a DAC that is rated 109db dynamic range and one rated 112db when even the test equipment has to be well calibrated to see it.
SNR is not very important in music. Especially at close listening locations. It's much more important in home theater where output levels are high.
Specs may not be entirely accurate from device to device...at 109db or 112db SNR, when your output hits 109dB or 112dB, distortion will have equal output of the original wave form. Not sure how it will sound, but theoretically it would be complete jibberish. It really becomes an issue of sitting distance from the TV, since every doubling of distance reduces output by 3dB. Obviously if you have an extremely large room and you are aiming for THX reference levels, a 109dB SNR DAC will not meet your needs.
Some audiophiles seem to consider the internal DAC of HK AVR not as good as some other DAC. And some claim the sound card DAC's to be decent. I could not tell.
If they are sitting 3-5 feet from their speakers, listening at reasonable levels, DAC is not that important (unless the specs are overstated). Of course, most of the specs are usually measured at the chips native sample rate (aka 24/96 or 24/192) so their performance at 44.1 may be at a much lower level. The biggest part of sound quality is in the gain stage and the quality of the pre-amp IMO, followed by the ability of the power amp to pump out current and a friendly distortion profile (less higher order distortions).