So long as the audio is balanced/differential on twisted pairs (preferably STP), and the cables have been routed sufficiently far from the nearest mains cables, this actually doesn't sound like it was a terrible idea. Power-over-Ethernet (which this pre-dates) can drive 25W DC over Cat5, so this probably does similar. It's certainly theoretically possible to make a decent audio output from 25W DC and a balanced audio input, though as Tony says it depends greatly on how good their wall-unit amps and their speakers are.

Peter