I have been using a Adcom GTP 860 for several years with a DirecTV MPEG2 HD reciever connected with coaxial, and its always been fine. Recently I upgraded to the new MPEG4 D* box, which only has optical. When I connect that, sometimes, for no reason I totally lose audio, although the Adcom still senses a Dolby Digital bitstream present. Changing channels doesn't have an effect. Then it comes back with a HUGE pop.

I connected the optical cable through a Audio Authority switch that converts multiple inputs to coaxial out. Even when its in this switch and connected to the GTP with coaxial, it still causes loud pops and other problems. Removing the optical cable fixes the problem.

Any ideas? I'm pretty stumped!