Is there a residual voltage on the copper? i.e. the standard BT lines show c 50v DC. My pal's line went very noisy and caused him much grief. I measured the voltage - in fact, left a DVM on the line - and we saw voltages as low as 10.
I have no knowledge of the signal conversion from optical to copper. One would think it required a black box, or part thereof, for every house.