The DACMagic has DAC processing more at the level of 740C not the 640C. Though all three use the Wolfson WM8740 DAC chips, the 740C and the DACMagic have more refined upsampling and filtering methodologies in place.
Do you remember the old days when the record player use to skip, or the tape player would play at a slower speed? These were the worst nightmares of a vinyl system or a tape player.
Digital storage and transmission of data do not have these issues, but have a slightly different problem. A digital data has a finite quantum of information that is exact in nature. This information is read by, say, a CD Player, and sent to an amplifier in digital form. The amplifier reads the digital data, converts it into analogue form, amplifies it, and plays it on our speakers for our ears to understand.
Now how do you send digital data from one end to another of this chain? Using electrical current which are called carrier waves. Now the carrier waves by themselves are useless. So you add the digital data as 'modulations' to the carrier waves. In other words, the carrier wave is modified to represent the data we want it to carry. Modulation is the process of varying some characteristic of a carrier wave with an external signal. The carrier waves are generally electrical current in physically connected devices, or radio waves for devices that are far away from each other. In both these cases, the basic characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal.
Now take the first case - of a CDP reading the data from the media. If the data in the CD and the one that is read is different even by a tiny amount, we have what is called 'jitter'. This difference could be just a few bits, but in the highly accurate digital system, this is supposed to be enormous. Now let us assume that the CDP has read with 100% accuracy. It sends the data to the amplifier through a carrier wave. Has it reached across with the same 100% accuracy? If not we again have jitter.
Jitter is, thus, any variation or dislocation in the pulses of a digital transmission. The usual causes include connection timeouts, connection time lags, data traffic congestion, and external interference.
The key to understanding jitter vis-a-vis digital transmission is precision, or acuracy of data. As digital information is sent out in small packets, if jitter occurs, synchronization becomes a problem and the receiving unit finds it difficult to correctly assemble the incoming data stream. Jitter can occur in both transmitting and receiving ends.
Generally to avoid jitter, devices use a localised buffer. Here the incoming signals are assembled before being used. This also gives the receiving station time to ensure that the data is accurate before it uses it.
Advanced CDPs read the same data packets multiple times and compare the copies or what are called 'samples'. If there is large amounts of similarity, it is happy. Else it will read it again. If needed, it reassembles the data from the samples to create the correct data stream.
In computer transmission, when the data is transmitted from one end to another, the carrier wave carries a checksum which allows the receiver to calculate the accuracy of the data received. If not, the receiver instructs the transmitter to resend the data. In audio and video, as they are in real time, this is not possible. Unless there is complete loss in signal, the receiver can use advanced mathematics to interpolate and guess the missing data.
Now what we are talking about is a loss or difference of a few bits. Sophisticated CDP, amplifiers, and DAC have the capability to compensate for these losses. Our ears will not be able to discern the loss, and in most cases, the music will sound as sweet as ever.
This is because the DVD player may not able to read with the same frequency range as the CDP. That is all.
If I were using a 740C, I will be walking with my nose in the air. Not feeling inferior at all. The 740C is one of the best players in the world in its price class. Keep your CDs clean, and wipe them before using. Similarly use good cables, and keep you CD Player and amplifier covered when not being used.
Beyond this, I would suggest you forget about all the technicalities of 'jitter' and enjoy your music.
If you are curious, please also read the following link where I have explained jitter within digital circuits.
http://www.hifivision.com/audio-video-cables/2959-noob-question-sub-woofer-cable.html
Cheers