CD Player? PC Music? Naaa Flash Memory Music.

Probably because the data is send to the DAC in a LAMINAR WAY?

04-01-12: Fmnp
I don't dispute that the s/pdif could introduce some jitter. But it will much, much less then that introduced by the optical device, mechanical parts and vibrations, Power supply, correction errors, angular velocity corrections, etc, etc. and time misalignment.

Since introducing the radically innovative Ayre D-1 DVD Player in 1999, we’ve been a leader in digital audio technology for the succeeding ten years. Yet in all that time Ayre has never offered an outboard D/A converter box, instead concentrating on one-box disc players. The reason for this is quite simple — the standard S/PDIF (Sony/Philips Digital Interface Format) digital connection used with two-box solutions is flawed, unavoidably and needlessly introducing jitter into the audio playback system.

And it would be something to prove that the toslink S/PDIF introduce jitter (at lest, audible). Why? there's no RF interference (unlike coaxial).
Ask what the studios use in there's SPDIF connections.
The only losses could be the quality of the fiber or the lengh. But with so small lenght's (1 to 2 m)...

Another interesting thing about audibility of jitter is it's ability to mask other sibilance in a system. Sometimes, when the jitter is reduced in a system, other component sibilance is now obvious and even more objectionable than the original jitter was. Removing the jitter is the right thing to do however, and then replace the objectionable component. The end result will be much more enjoyable.

Jitter can even be euphonic in nature if it has the right frequency content. Some audiophiles like the effect of even-order harmonics in tubes, and like tubes, jitter distortion can in some systems "smooth" vocals. Again, the right thing to do is reduce the jitter and replace the objectionable components. It is fairly easy to become convinced that reducing jitter is not necessarily a positive step, however this is definitely going down the garden path and will ultimately limit your achievement of audio nirvana.

04-01-12: Fmnp
I believe that this article shows that I'm right.

04-01-12: Fmnp
I don´t know what are the technical reason's that you mentioned but I'll be glad to read them.

... the standard S/PDIF (Sony/Philips Digital Interface Format) digital connection used with two-box solutions is flawed, unavoidably and needlessly introducing jitter into the audio playback system.

A low-jitter master audio clock is essential for attaining high performance levels of digital audio reproduction. But that low jitter only matters at one critical point—at the D/A chip itself. Jitter-induced timing errors create artifacts that audibly degrade the music signal. Therefore a well-designed one-box disc player places a fixed-frequency master audio clock right next to the D/A chip for the best possible performance.

In contrast, a two-box system splits the system into a disc transport box and a D/A converter box. The two are normally connected with the industry-standard S/PDIF connection which places the master audio clock in the transport box, where it is mixed together with synchronization codes and the audio data and transmitted to the D/A converter box. The D/A converter box must then attempt to recover the critical master audio clock from this jumble of signals for delivery to the D/A chip itself.

The standard solution for a two-box disc player is to use a PLL (Phase-Locked Loop) to control a VCO (Voltage-Controlled Oscillator) in the D/A box, generating the master audio clock. The VCO varies its frequency in order to lock onto the incoming signal sent from the transport box. Unfortunately, a variable-frequency oscillator simply cannot achieve the low-jitter performance of a fixed-frequency crystal oscillator.

Over the years many schemes have been implemented by various manufacturers in attempts to improve the jitter performance of the S/PDIF connection, including dual PLL’s, VCXO’s (Voltage-Controlled Crystal Oscillators), frequency synthesizers, FIFO (First-In, First-Out) buffers for the audio data, external re-clocking (”jitter reduction”) devices, and so forth. While all of these methods are able to reduce the jitter levels, they cannot eliminate the jitter that is inherently added by the S/PDIF connection.

Another approach to reduce jitter that has become increasingly popular in recent years is to use an ASRC (Asynchronous Sample Rate Converter) chip. The idea is that the original audio data is replaced with newly calculated data that represents what the audio data would have been if the incoming signal had most of the jitter filtered out. The technical theory behind this method is sound, as demonstrated by the measured performance, which is generally quite good. However the audible performance of these devices is controversial, and Ayre has avoided this approach as it completely discards the original audio data.

Why flash drives, not CD’s? Because the big problem with the Digital Music is one thing called jitter. And with this solution you throw away the major source of problems in this matter. Optical drives and their Digital MASTER internal clock’s.