Knowing a "goes dead" time frame would be a great help here.
Does your stereo work with the key off? If so, rewire it correctly. Even with the power switch off, most car stereos will draw more power via showing the clock or keeping the face lit than they would with the main power wire connected to 12V key-on. This is especially true of newer stereos with "soft start" (tactile) switches and ridiculous multicolor demo modes. Any digital car stereo has two 12V+ inputs: one is typically yellow for station/position memory and clock (if so equipped); the other is main power and is most-often red. The main power wire needs to go dead with the ignition key. If you want to listen to the stereo with the car off, there's an "Accessory" position on the ignition switch for exactly that reason.
'Twas a common repair to make way back in my installer days, along with Scotch-Lok/wire nut/twist-and-tape connections, speaker wires bodged into RCA inputs, and other common "I can do it myself" errors made by people who clearly couldn't.
If a parasitic load test results in a popped fuse in, or the destruction of, your DMM I would expect your battery to be dead every time you tried to start the car (unless you left the lights on during the test by accident). A drain greater than 10A will drop a car battery below starting capacity in a few hours. If the drain's that bad, you've got a major defect in your wiring or equipment.