Hi Don - Welcome to the forums. I can try to answer some of your questions. In the most general ways, materials for example, there's not a lot of difference. The main difference between digital cables and analogue ones has to do with the impedance, and then might differ in construction in order to maintain that impedance. An AES/EBU digital cable should fall into the range of 110 ohms and is a balanced digital cable, using XLR connectors. An S/PDIF cable is single ended and should be 75 ohms. There are + and - % allowances for both. Some of the confusion that may arise probably comes from the outward appearance of analogue cables with RCA connectors and S/PDIF digital cable using RCA connectors. An RCA connector is not really designed for the specifications of S/PDIF. The thing to remember about S/PDIF 75 ohm digital cables is that the ratio of inner to outer conductor diameter in the coax (or connectors) determines their impedance (in this case, 2:1) as long as the dielectric constant of the insulator stays the same. A BNC connector, because of its construction is able to maintain this ratio. With an RCA connector, it's virtually impossible to do this. Unfortunately, there are few companies that use the superior BNC connector.

This is a clear explanation of the above:

http://www.bluejeanscable.com/articles/75ohmrca.htm

The design for digital cables has to be more stringent to maintain these impedances. Analogue cables can vary far more in terms of construction. Goertz ribbon cables have very low inductance, but extremely high capacitance, which makes them poor candidates for hooking up to a turntable (I've tried and the squealing is unbearable.)

Because of the delicate signals involved in the phono stage, I'd think a nice shielded cable would be preferable. But, I know my friend Wes likes Kimber KCAG for phono, and that's a tri-braid construction that relies on its braiding for shielding as opposed to having typical shield. Knowing his preference, I tried a similarly constructed silver cable for my own setup, which I now currently use. The are endless possibilities and solutions... no one construction is going to be right. You need to try out different cables and find what works in your system.

Don, you're welcome. As I recall, some of the cables in Audioquest's line use PVC sheathing, which is a less than ideal insulation. If you still have product literature on your cables, check to see what dielectrics are used on yours. If you have PVC, it's definitely worth giving a listen to cables using Teflon insulation.

Hey Don, when you do reintroduce the Audioquest cables into your system, they will have been in storage long enough to need another 100+ hours of current to sound right again. They will sound just awful in comparison to fully settled cables and you might be tempted to yank 'em out too early.

Don - Hopefully your sound will improve after running signal through the cables for a hundred or two hours. I usually try to stay away from analogue and digital cables using PVC... they often sound smeared and unfocused to me. It's possible the boominess you're hearing might partially be caused by the PVC insulation.

I posted some related thoughts/info here:

http://www4.head-fi.org/forums/showthread.php?p=1984354#post1984354