Which cable to use on Aleph internal wiring?

According to the formulas, skin effect only begins to be important at RF frequencies. However, if you try, say, 10 ga. solid core (only--no other strands) as an interconnect on a decent system, I think you'll find that it does indeed make a difference at audio frequencies. This is a clear example of one of those "numbers don't tell the whole story" situations. Enough of those and you begin to look at audio and so-called "snake oil" upgrades in a different way. Some of them actually matter.
One of the things to remember regarding strands--if insulated--is that it increases the capacitance, which begins to tailor the frequency response. In a worst case scenario, it can cause oscillation and blow amplifiers (happened frequently back in the '70s). Moral of the story: There's a balance to be struck between the number of strands, their gauge, whether they're insulated or not, composition of the wire, composition of the insulation, etc.