your insurance company should offer a rider to your auto policy to cover an aftermarket audio system. they usually charge a small fee for the additional coverage. an alarm will lower your rates too. as you noted, don't attract attention, if you choose, use silent arming for the alarm so it doesn't chirp. always keep the car locked. have the equipment out of sight, and securely mounted. keep the car parked in a garage, or well lighted area. record all product serial numbers, and keep them with all of your receipts along with photos showing teh install, and the item serial numbers.
if you do buy an alarm, get a good one. and have it put in professionally. A cheap, poorly made or installed alarm is just about worse than no alarm at all.
You can make it more difficult to steal, but pretty much anyone with a system that is even semi flashy will get it taken if they live in a big city....
atleast thats been my experience
if i were you i would just get a stealth box and keep everything hidden under seates etc
i had a crv with a stealth box and amps under the seats and it never got stolen....until i had to get it worked on at the body shop....inside job just used my alarm clicker and took everything but they still couldnt find the jl stealthbox lol
they had to get me all new stuff for free but it still sucked
i was talking to my dad abuot this topic the other night about what would happen if my stereo system was stolen, he had said that under our particular insurance there was a clause in our home owners that said something to the effect of anything of your property in your possession (ie car, house shed) will be reinbursed in full with proof of ownership. like a receipt, picture, credit card statment...something to that effect.
i work for an insurance company in california. we can insure up to 5000 dollars in any tipe of optional equipment, with full coverage on a vehicle for around 30 bucks a month. all they need are receipts on file, and , in case the stuff gets stolen, u make a claim to the company and get the money back for what ever gear was stolen.