Does any 2012 Audi A6 owners with a 3.0 engine experience brake spongy feeling and having to press too far down to get to stop vehicle then on occasion brakes lock up and almost lose control of vehicle?
Whether or not others have had this problem, which I sususpect is yes, you need to get your car in for repair. What you are describing is very dangerous.
Have you had brake work recently?
If so you may need to return to the shop that did the work, and have them bleed the brakes.
You could also have a leak in a brake line and every time you press down the brake pedal you are pumping part of the brake fluid out the leak.
Before you try to drive this, be sure your brake fluid is at the proper level, or you may get half way to the shop and have no brakes at all.
This should actually be towed to the repair shop. Brakes are something you do not want failing.
Spongy brakes are often a symptom of having air trapped in the hydraulic system somewhere. Bleeding the brake lines could probably solve that problem if it was your only problem.
On the other hand, having the pedal engage at a lower height is often the sign of a malfunctioning brake master cylinder, and I don’t know what could be making them lock up if it isn’t you.
It sounds like the car is unsafe to drive, but if you insist on driving it, drive it straight to the shop and tell them about the symptoms. Leave out my armchair diagnosis if you want unbiased diagnostic work.