I like to read your explanation, I'm learning a lot, but on the XLR (Balanced part) there is one thing that I don't understand, how there could be an impact even if there is some noise going into the cable since basically the way I understand it, there is 2 opposed polarity, so the transformer at the end and subtract what was added during the transport. Wikipedia explain it better then me:
My DAC and my amp are connected with 2 x 3 pin XLR cable (one for left and one for right) I'm currently using short 3ft Digiflex professional with neutrik connector.
My T1 really sing on my setup, I can't stop listening to music, I have discovered the "lossless" and "HD" track, I enjoy it big time.
As for the USB cable, I use a cheap 10ft $3 Startech cable with little to no shielding to connect my DAC and it works well. My usb cable go behind my desk and follow I don't know how many other 120volts wires and I don't hear any noise if a track if perfectly silent even if I set my auditor to the maximum (which would blow my headphone if any sound were played).
Let me see if I understand your question. Are you saying that since a balanced configuration of cables and electronics is designed to cancel out noise so how can some noise still get in?
If so, here's an analogy. Basically, the higher the frequency (i.e., the shorter the wavelength), the smaller the holes it'll fit through. Normally the electromagnetic noise found in an audio environment is pretty low frequency. 60Hz hum off of power wiring, ballast noise from florescent lights, etc. Running a microphone across a stage with a 60 foot long cord will typically see a bunch of this stuff. However, digital clocks in computers and DACs can run at much higher frequencies. Higher frequencies can just get into things easier.
Regarding you system, it sounds like it's working well for you. I wouldn't worry too much about it if it's giving you a lot of pleasure and you aren't getting any subtle artifacts that might be due to jitter. Some thoughts on your lossless and HDtrack stuff:
1) Lossless is a compression method designed so that when decompressed, the original information is all there. However, it adds an addition step in the conversion of the data during playback. If you use uncompressed files (e.g., .wav, .aiff, or FLAC), you remove a level of digital processing. Theoretically, it should make no difference, but I did on some rare occasions hear a difference on a system I was using. I have no idea why it occurred. Perhaps my core audio in my computer always digitally filters (i.e., anti-alias filter) anything that goes through it and I know that that definately has a degrading effect on my system. So try experimenting with some non compressed files. If you don't see any reason toe retain the uncompressed formats just remember that some of the lossless formats are proprietary (such as apple's)
2) The HDtrack stuff (i.e., the high resolution files). There is some debate over whether or not high sample rates really buy anything. My jury is still out on that, but I have also heard that some of the hi sample rate tracks were actually mastered at a lower rate and then upsampled to create some of the files that they sell. that buys you nothing but just takes your money and uses up space. Also, If you check out the "Sennheiser HDVD800 Headphone Amplifier" thread and go back several weeks, there is a lot of discussion about ultrasonic noise that has been left in many of their 192kHz sample rate files. This noise is not supposed to be there per standards as it is way up above the Nyquest frequency and when the file is played back the ultrasonic noise creates audible noise that is like a loud hissing during the playback (these are aliasing artifacts) When Sennheiser built their HDVD800's DAC they were choosing to minimize as much processing on the digital data as possible. As a result this ultrasonic noise gets through and makes the recording unlistenable. For me, this currently corresponds to half of my HDtrack items. Most companies have put in anti-aliasing filters in the front end of their DACs to avoid this problem so you won't hear the problem on many DACs, and in fact, Sennheiser is in the process of creating a firmware update to fix this problem on their HDVD800. they want to set it up so that it only runs the filter if there is actually noise in the recording. That way they can still use the minimalist approach for the clean files. The thing that irked me is that HDtracks is selling files that do not meet industry standards. The combination of these issues have led me to decide that if I buy any more hi-rez tracks from them, they will only be 96kHz or lower.
3) I have a T1 with a HDVD800 DAC/amp combo who's total value is around $3400. I am using a Monoprice 10ft USB cable that was $1.49 if I remember correctly. I have compared it with a $500 Audioquest Coffee USB cable and can't detect any differences. But my HDVD800 runs USB Asynchronous transfer mode so In general I don't expect to see any difference.