I have some dB Systems DB-6 power amplifiers (four in all). One of these is circa 1980 and the others are circa 1986 or so. All have been modified (back in 2005 or thereabouts) by David Hadaway of dB Systems; I had three of the DB-6 variants converted to the 6M variant (mono-block) as well as equipped with differential XLR inputs (which work nicely with the 990's balanced outputs). The last DB-6 was left as a two-channel amplifier (but modified to have differential XLR inputs) and those are used for the surrounds.

They have been extremely reliable and are about the quietest amplifiers that I have ever heard (i.e. very low noise floor) and certainly the quietest that I have ever owned. They drive B&W Matrix 805's in the main system.