To quibble just a little–a number of successful early NLE’s were PC based. Lightworks and the Montage3, which used Intel’s ActionMedia card, were both successful film/tv NLEs out here in LA at the beginning of the 90s, and certainly drew people to use them.
As for 1st broadcast quality, my memory tells me that it is something like the old DPS PVR card and maybe Speed Razor on the PC. Hard to check with Google, though, as what conversations existed were on extinct bbs and services like Compuserve. Man, I used to love Compuserve.