The only place I know of that offered ICE specific insurance was Firebond, but I've heard from several people now that they're not taking on any new policies.
Also, given that the cost of the insurance is 10% of the value of your ICE equipment, that you have to provide receipts for anything you're insuring, photos of everything installed, the excess is around 10%, and that you can't cover wiring/sound deadening/labour, it doesn't work out that great of a deal anyway.
Say you have £2k's worth of equipment, and £500's worth of sound deadening, wiring, distribution and so on (and I know that you have atleast one thing that wouldn't be covered, whether I gave you a receipt or not), you'd be looking at £200 insurance, £200 excess, so that's £400 for one claim (then you have to consider that the premium would go up next year). Would it really be worth claiming? Well, they'd have to grab a substantial portion of it to make it worth it anyway.
So basically, the answer is "make it stealth, and cross your fingers".