I have a question regarding ground for my electrical AV equipment. I live in a 1930's house and it only has two prong outlets. All of my equipment is plugged into a power strip that goes into the wall. I fitted one of the 3-->2 prong adapters so it has no ground. Equipemnt plugged into this strip are a 46" LCD, Pioneeer RX-V1400, Denon DVD2200, and a HTPC. All the equipment has been running like this for about three years with no issues. I'm getting a little paranoid about protection for it though and plan on adding an APC H15 power conditioner.
My question is, what are the risks of running the setup like this without a ground? I live in CA and not in an electrical strorm area. I'll also be adding an Emotiva MPS-2(no worries I have M60s \:\) ) into the mix next week.

Any info would be greatly appreciated, I don't have much knowledge in this area.

Thanks in advance \:\)