I can answer questions about the electronics and mathematics behind car stereos, provide information on locating wires, wire interference, gauges, etc. Since they're almost entirely subjective, asking questions about brand names may not result in the most useful answers.
I've been installing car stereos for friends and family (albeit not professionally) for 8 or 9 years. My knowledge lies mostly in the math and technical aspects: impedance, required gauges, fuse levels, frequency response, etc.
The school of, "WHY THE HELL DID YOU DO THAT?!"