Hi Bob,
As far as I am aware Transparent and the other makers of cables that incorporate network boxes haven’t ever published schematics or other detailed information defining the circuits that are in those boxes. Without that kind of information, and conceivably even with it, I can’t provide a meaningful answer to your question.
But in any event no such box will convert the wire that is being used into a transmission medium that is theoretically ideal (i.e., zero resistance, inductance, capacitance, dielectric absorption, etc., at all frequencies that could conceivably be relevant), and so the same kinds of considerations that have been stated above for boxless cables would seem to apply, albeit perhaps to a different degree. As well as the same dependence on opinion, since as I said earlier it can be presumed that "no comprehensive body of experimental data exists on this question, encompassing a broad range of systems, rooms, listeners, and combinations of cable lengths."
Also, although it doesn’t necessarily directly relate to your question, I’ll add FWIW that I would imagine that in at least some of those cases the values of the parts in the boxes (ohms, pf, etc.) might be chosen differently for different lengths of the particular type of cable.
Best regards,
-- Al