a) just hitting record on the d8 (not pause, etc.) should not load the tape and the deck should act as a pass-through indefinitely.
b) a computer has a LOT of rf noise going on inside of it. A soundcard that performs a>d inside of the computer would likely lack the shielding, etc. necessary to avoid having the analog signal be adversely effected by this rf interference regardless of its resolution. Thus, I'd agree that analog>d8>digital>soudcard would likely be superior sounding to analog > internal digital soundcard.