Also got this input...

Basically, you want your Z (impedance) either equal or much greater than the output Z of the box sending the signal. Usually for high-bandwidth signals (not analog audio, but definiteley digital audio) you want the Z's equal, and they will usually be 50 or 75 ohms.

For typical audio, you probably want to send into the highest Z you can. Higher Z on the input device will make you more noise sensitive, so if you have noise pickup issues try the low-Z setting. Low-Z will eat more power from your output device, so may reduce battery life, though I would think not by too much. Using low Z may reduce the volume you hear, so if it seems like the volume is too low, go back to the high Z setting. If unsure, use high-Z input since the output device may not be designed to work well into low-Z and may distort.

If you have an electric guitar w/piezo pickups without an internal amp, use high Z for sure. If there's an internal amp of some kind, either will probably work, may well be designed for low-Z. would need to see the manuals to be sure.

470k is plenty of input impedance - no need to jack that up with anything else.

Hope that helps-