Once upon a time, if you'd asked a Korean (go on! Ask a Korean!) which of their uncountable legions of musical luminaries was most likely to crack the blast-hardened firewall of the American market, they'd have offered up curvaceous crooners like Lee Hyori or BoA, floppy-haired dreamboats like Rain or Kim Hyun Joong, or mega-girl groups and boy bands like Girls Generation and Super Junior.

And why not? These finely tuned, precision-machined performers represent the pinnacle of technology in a market that has transformed the...