Getting Personal Property Insurance for your rig.

I just had an Allstate agent tell me that he's sorry, but they're unable to insure my "$120k stereo".

Do any of you have personal property insurance protecting your system against fire/theft/etc?

If so, how did you go about getting it and who did you go with?

Has anybody had to file a claim?
I have spoken to my insurance agent who told me my particular policy does not cover systems of this nature, but some policies do not have these limitations on categories of personal property.  For now, my system is more or less not covered, the caps are so low.  However, my agent told me that when it comes to renewal time, we can find an insurance policy that does not have any particular category limit, and personal property will cover it, with proper documentation.  

Call and and talk to different insurance brokers rather than insurance companies themselves and you should find what you are looking for.
Renters Insurance covers personal property, but your company may not write policies to that limit.  Mine is about 50K, also through Allstate.  You will have to find an agent that can write a renter's policy that high.  
High end stereo would fall outside the normal parameters of Person Property on a standard HO-3 Homeowners Policy. You need to put it into a special "Scheduled Personal Property"  (sometimes called a Property Floater) endorsement. This same endorsement is designed to cover jewelry, expensive art, furs, coin collections, etc....This is an "All Peril" endorsement, meaning it’s covered and paid for even if you simply can’t find your $35000 Rolex anymore. The fraud rate is assumed to be very high, so the rates built into this endorsement are designed to compensate for the folks who commit felony fraud and cheat the system.
Whichever way you guys go, make certain your collection is insured to the hilt. Insurance companies will try to screw you come claim time!
Many years ago I had a "visitor" help himself to my audio system.  I had photos of my system and receipts for the items I purchased new from a store, with serial numbers and they paid claims for those items, but did not pay for the speakers I purchased used.

At a minimum, I'd say having photos and serial numbers would be a good thing to have.

With an audio system of that value, I'd check the policy limits on your homeowner's personal property coverage, and whether it has exceptions.  I once discovered, buried in the small print, that my wife's jewelry would not be covered, so we purchased a "rider" to cover that.