As far as I know, Threshold was founded about 1974 by Nelson Pass and Rene Besne. In 1988, it was acquired by a big corporation. Besne left the company in 1991 and Pass left in 1992. Thereafter, it appears Threshold's products were designed by Michael Bladelius, Wayne Colburn and others. Later Wayne Colburn became vice president for design at Pass Labs. Why did Threshold fail? The only symptom I see is that beginning with the "e" Series, the fullest realizations of Pass' original designs and introduced in 1990, everything acquired a part number, even the manual! A case of micro-management? Maybe. The later "T" Series amps used IGBT output transistors (as opposed to Mosfets) which are no longer available. As far as risk goes, the prices of Pass era Thresholds appear to be rising.