Pete10:Do not know this gear, but I suspect the Topfield is sending a type of digital signal that is not supported by the DacMagic (5.1/7.1/dolby?). Try to find the output options in the Topfield menu system and see if you can select simple stereo to start with for its digital output. Does the dacmagic have a led that indicates it has locked onto the received signal?
That's where I was going, but your bog-standard Topfield appears to have only stereo or mono, hence my disconcertion(?).
And yeah, the Dm has a light saying it has a signal and what bitrate it is.