The Modius is a delta-sigma DAC with a switching power supply. Both of these help save money.
The Bifrost is a true multibit ladder DAC with a linear power supply.
On the Schiit web site, read the FAQ tab for the Bifrost. It gives a basic explanation of why Multibit (ladder) DACs are better than the delta-sigma DACs. With a little searching, you can find further discussions on the issue.
