You have more good questions. Good!
I was afraid you would have no way to put a resistor in your N-scale
As far as what resistance the command station needs to see, the
lower the motor's resistance the better. Now, I am pretty sure that
you said the programming worked with the motor that had the higher
resistance. Don't panic. Measuring a motor's resistance is
actually a poor way to determine how much current the motor will
draw while running. How much current a motor will draw is based on
it's running REACTANCE. It is possible that your motor with the
lower resistance has a higher reactance than the other motor. So
don't waste your time measuring a motor's resistance.
As I see it, you have three choices:
1. Check with Digitrax and ask them if there is a way to increase
the sensitivity of the command station to a decoder's
2. Program the decoder without being able to read the CVs as I
indicated in an earlier portion of this thread.
3. Program the docoder using a different motor or a resistor.