Welp, against all better advice, I installed the Preview for Developers option to get 8.1 on my ATIV. Sure enough, all external sound stopped working. Outgoing calls work fine, BT headset works fine. I'm not certain of this yet, but it seems if I miss a call, the screen becomes unresponsive, and after a reset, I'm constantly asked for my PUK. On the verge of a factory reset now.
I am up to 1 Day and 14 hours of up-time. No crashes, consistent WiFi connections, no non-responsive touch screen. I'm in awe of how stable the phone is. I'm wondering if they pushed some kind of firmware update along with the 8.1.1 update. Unfortunately I don't know what my previous firmware version was. Right now I'm at 2218.14.03.2 if anyone wants to compare.
After two days of stability I catch lockup and reboot, and this happen when I listen music via bluetooth in my car (twice). My old Ativ S has same problem with bluetooth on 8.0 and 8.1! Samsung suck! sorry for my english.