Quote:
Originally Posted by
landgreen 
Does changing the volume level in Itunes change the data flowing from computer to DAC in any way other than volume?
Moving the volume slider in iTunes will change the data. iTunes will take the digital audio and scale everything down to be softer before sending it to the DAC. It is a lossy conversion, though the loss may not be noticeable. Unless you have a reason to do otherwise, I suggest leaving it at 100% and let the amp handle the volume control in analog.
But if you do have a reason, such as channel imbalance when the amp volume knob is too low, then by all means lower the iTunes volume. Channel imbalance is a worse problem than the theoretical loss of resolution from lowering the volume digitally.
Quote:
Is there significant difference using an expensive USB cable to the DAC? ie Is there any data loss with "normal" USB cable?
There is a specification that a cable must meet to be considered a proper USB cable. The cable must be shielded, and the two data wires inside must be twisted together separately from the power wires. If a cable meets all the requirements, I'd say that's about as good as it will get. Some expensive boutique USB cables look nice but don't meet the specification. So if you are looking to buy something fancy, at least make sure it is up to spec.