This is a short summary of my setup as used at home, i.e. mainly for practice/training as a hobby.
Below, you will also find a simple way to work around the limitation of the TC Electronics RH-450 amplifier head not being able to mix the AUX signal input into the speaker out signal (limited to headphone usage only), which is just too bad for use as a practice amplifier
The basses are:
The cabinets are Hartke HY410 and a Hartke HY115.
This section contains:
The setup is cabled as illustrated in the following diagram (more detailed PDF version here):
The detailed photo of the combined mix-to-mono cable / headset splitter cable below with the resistors hidden inside heat crimped insulators