I am running a zoneplayer with a sonance 275amp to wired outdoor speakers. Even at full volume the speaker output is quite low (fixed and variable settings tested). When I connect another source, like an iPhone, to the sonance, the volume can go dramatically higher. I’ve tested with two different zoneplayers and two different amps and the result is the same. Also tried different cables. Leads me to believe the line out on the player is the issue but not sure. And there is no line in being used where I could adjust the line in. Has anyone had a similar issue and figured out a resolution?