Hi . I have had a Marantz PM68 Amp for the last 6 years now. I have it connected to a CD player (also Marantz), the Sky box and a DVD player (Sony) .. connected to Cambridge SoundWorks bookshelf speakers. Recently everytime I put the volume up - the amp cuts off for a few seconds. This has happened with all 3 imputs. Today I went to replace this amp (thinking that the amp was the fault) with a Marantz PM4400 ... and the same think happened ? Please help . . is it the speakers ? the spreaker wires ?? ..