Given your description of the Wadia's poor sound quality, I have to assume that you are comparing it to another transport feeding you Bryston DAC; probably a CD. The first thing that comes to mind is what format are you using? If you are playing something like MP-3's through the Wadia and Redbook with another transport, that could easily explain your results. Also, Pass makes a wide range of amps; some powerful, some not. Its possible that the amp is having a difficult time with the Magnepan's and not the Harbeth.
This may sound odd, but one other thing I would definitely try is unplugging all other components that are not in use when the Wadia is playing. Especially digital components. If that makes an improvement, you should be able to hear it right away.