You didn't lose a 6 year old Sony deck. You lost the ORIGINAL Bose radio. The difference in price should allow you to cover your deductible and leave you enough left over to buy a decent aftermarket system again (maybe? Haven't priced the Bose radio in a while. I once had a cheap Alpine stolen out of my Nissan pickup; the dealer said "You should've filed a claim for the original radio; it's $700." Why should you get robbed twice? Especially when all you want is compensation for what was stolen?
And don't forget to write off the theft losses on your taxes next year if you itemize.