Stumbled upon a link to AMP Research and it seems they are still going, however not making bikes any longer. Before you click the link have a think what you imagine they are making these days!
Also, there is a section on the company history with this in about mountain bikes
AMP RESEARCH MOUNTAIN BIKES
In the 1990s, Leitner turned his attention to innovating in the mountain-bike world, creating the now-legendary AMP Research full-suspension bikes. Characterized by Leitner’s revolutionary four-bar articulating front fork, energy-saving Horst-link rear suspension and the first cable/hydraulic bicycle front disc brake, these ultra-light, all-aluminum bicycles set the standard for mountain-bike technology. AMP Research also produced similar Mercedes-Benz bicycles, which were marketed through Mercedes-Benz dealerships in the United States and Europe. Leitner later licensed the Horst-link technology to Turner and Specialized Bicycles, which is the design foundation of their full-suspension mountain bikes.
Really interested in the bit about Leitner licencing the horst link out. never realised that before. Must be a nice little earner for them. Really surprised they havent tried dabbling with bikes again in house though as they have a name established and the licence for horst link, seems like a nice business opening for someone to go in and run the operation under their banner!