X6 is a ton of money. Enough so that a reliable home security system combined with a lesser safe is probably the more realistic option. If you have a large collection, the cost of stuffing it in TL15 safes gets huge really fast.Once you get into UL rated safes in the TL15x6 or TL30x6 category, a regular angle grinder wont get you far. A demolition saw with abrasive blades or a professional core-drill will get you in, but not the kind of stuff you find in a homeowners toolbox.
All it takes is money.
This really gets overlooked a lot. Once you hit TL30x6 (which isn't the same as TL30!) talking about safes that exceed a ton in weight. Moving them in is a beast of a problem, too.... and concrete to pour the extra foundation you need for a TL30 big enough to hold long guns.