I have a receiver that has digital coaxial outputs for each of my speakers ...
Are you sure they are designed to feed speakers?
What kind of receiver?
The only digital output that I am aware of is the S/PDIF output which is a low level multichannel electrical (coax) or optical (TOSLINK) output:http://en.wikipedia.org/wiki/S/PDIF
The S/PDIF output would need to be decoded and amplified (something that already happens in your receiver) to drive the speakers. They cannot drive speakers directly.