I used to have an AU-717 amp which was a great bit of kit. A real powerhouse. Built like a tank, but a delicious sound quality to it. It bettered an Exposure 3010s, Harman HK990 and was easily the equal of a Leema Pulse I tried out at home. The thing hadn't been serviced, so I took it in to have it done by a local audio repairer who knew his stuff. The caps are famous for leaking, the circuit board is sometimes corroded thanks to the type of glue that Sansui had used at the time. This would always be my first step with one of the better Sansui amps. The AU666 predates the -17 series amps, so it might be in need of a good tidy up under the lid.