66 blocks have and still are being used for voice. They are not suitable for networks.
The very first place I would start is to find the REN that the VoIP box will support. The second thing I would do is to find the REN of each of the phone devices in the house.
What is REN? REN is the Ringer Equilivelency Number.. The old 500 style phone has a REN of 1. You NID may have a 1/2 ringer installed in it. If it does and hasn't been disconnected from the house, count that as 0.5.
The VoIP REN that it supports must be greater than the REN of the devices. Remember to count separate bells as well. Standard phone lines support a REN of 5.
This is where I would start.
See this:
PAP2T REN capability problem [Archive] - VoIP Forums, Internet Phone Service Forums, & Web Hosting Forums
Have all of the filters been removed (Maximum is 5) or were you/are you using a single splitter for DSL or preferably no splitters at all in your case.
Is the DSL modem, the only thing on the telephone line? How is this wired? Quad cable? Cat 5? Haw far away is the modem from the NID? Have the other jacks been disconnected from the DSL modem circuit?