Hard to get something cheaper than $30 over here across the pond.
That same one is £20 ($35).
I initially used 10k resistors, but that reduced the volume too much for my test amp, so I tried 1k resistors. It sounded fine, and didn't seem to cause any mixing
before the signal went through the resistors. Would there be an audible difference if 1K was too low? Only the stereo amplifier would be directly connected to the laptop; the mono one will run from the same outputs as the mid/tweeters.