Several questions: Radio Design Labs makes a 10K combiner/divider that sums or divides line level inputs/outputs. Why is 10K a useful resistance to achieve this as opposed to something else? The spec sheet doesn't give a ton of information regarding the schematic--just resistance/impedance. Below is a link to the product.
Are the two primary considerations of a combiner making sure your interfacing impedance to the next input is appropriate and that you're not feeding the outputs back into each other/loading down the outputs, whilst trying to combine them?
what's the reason for making as high-as-possible resistance?