Do USB cables matter ?

It's only data copy. Any functional usb cable will do. Just like copying any kind of data on a computer.

I agree with Mapman 100%. All you are doing is copying data files from one drive to another. The fact that the bits in those data files represent music is irrelevant.

Although it would undoubtedly be a complete waste of time, if you want to satisfy yourself that the bits were copied accurately you could use one of a number of downloadable free programs that are available, such as this one (for Windows-based computers) which generate and compare file "checksums."

However one thing that could conceivably be desirable from a sonic standpoint, at least if you are using a Windows-based computer, would be to defragment your external drive after the files are copied to it. At least, that is, if the defragmenter program (which is built into Windows under "Accessories/System Tools") indicates a significant percentage of fragmentation.

If the computer is directly connected to the DAC, for example via USB, it seems to me to be at least slightly conceivable that some of the electrical noise which would occur during playback as a result of the hard drive constantly jumping around to read individual files that are broken up into diverse physical locations could ultimately find its way into the DAC and adversely affect sonics, at least slightly. On the other hand, though, be aware that defragmenting 6000 albums worth of data is likely to take many hours of computer time.

If the computer is a Mac, though, I can't speak knowledgeably on that potential issue.

Regards,
-- Al

Mapman, Almarg... this is good info. So, data is data to copy from one HD to another. That's great to know.
De Fragging the Ext HD... I would have never thought of that. Seems it would allow things to run smoother.

Almarg, does the program in the link you provided check as your copying data or after to validate the data ?

I'm planning to run my NAS HD to my Laptop via wireless router. From there, I'm going USB to Asynchronous DAC to Pre to Amp.
It's all new to me, but I can't pass up 6000 albums for free.

Just getting my feet wet right now. I may go with a dedicated server in the future. I want to take small steps right now.

JRiver with Fidelizer as an optimizing program is about as far as I have planed for this system. I'm hoping to at least get as good of playback as my CD Player.