My family...My house..heck my stuff. It stopped being a property crime once they entered with guns..
This is the biggest problem with the scenario, burglars do not enter houses carrying firearms in plain sight. Most burglars never carry a weapon or enter a house that is occuppied. With that in mind, I would have to say the lethality of the scenario is raised beyond the idea of protecting your stuff and my main concern would be protecting my family. Honestly, they could steal everything I own and I wouldn't care less, but I doubt that is the intention of two masked, armed men prowling my house while my family is in it. This doesn't look like a burglary, and my response would be in accordance with the threat. That is what my post earlier was stating, not trying to go 'commando', just trying to protect my family.
On a trip to reality, I doubt anyone could get into my house undetected anyway, and if they were good enough/well planned enough to do that, I doubt my response would matter.