I'm glad to hear that this seems like a good way to go. Jeff, unfortunately the only sources I have are my turntable and CD player, neither of which I want to run for a couple of hundred hours straight.
I picked 100KOhms because that approximates the input impedance of my amp. I've been wondering if I would actually be able to do a better job if I cut that in half. That would still be high enough to provide a decent high impedance source for my preamp, and as it is pretty much a resistive load I shouldn't have any trouble with any sort of weird reactance. Or I could just turn the volume up on my preamp, I guess.