I don't think you can conclusively state whether there would be appropriate resistance with the pre-amp turned off. I would think there would be a very high resistance. If you really don't want to turn on your pre-amp you could look in the owners manual of your pre-amp or search on the web to see if anyone has listed the input impedance of your pre-amp and go to the Radio Shack and buy an appropriate sized resistor. Like looking at Krell amplifiers they have a 100 KOhm input impedance.