How about Sigma's DP series of compact? Yes... these are using prime lens, but I have read incredible reviews for these cameras. In actual fact some even compared the IQ from a Foveon sensor to a FF sensor (like the Nikon's D800).
If you really want a compact with comparable or even better IQ as compared to DSLR, I think Sigma is the way to go. Oh... and the DP series of camera are really small in size too... except maybe the DP3 which had a bulging 50mm lens.
compact, fixed lens...assume you want zoom? RX100 for sure. being an NEX user, you will appreciate the entire system of the RX100...and of course, it takes really really good pictures. Fuji X20 is what i use right now (changed from RX100) and it's also a great camera, although for pure image quality, RX100 is a bit better
X100S, well...it's bigger, fixed focal length, and is slower in overall performance, from what i hear. I'd get the RX100 if i were you