A DAC should not have a "sound" signature of any type. The purpose of such a product is to convert a digital signal to an analog signal. There exists an analog stage with every DAC, but these rarely make any audible difference unless there is a fault with the unit under test. Also, a DAC can utilize filters for digital response that might alter the tonal characteristics on paper; though, in practice, and especially with regards to the chip used in the Modius, these would be difficult to identify between one and another.
The fact that the Modius and Bifrost share the same analog stage for balanced output and were designed by the same people, there is no excuse for there to be any major differences of any significance unless it is intentionally built into the design. I would not expect that from Schitt. The Modius' AKM DAC IC AK4493 is an absolutely awesome modern piece of audio technology.
Here are some measurements and comments about the Modius.
https://www.audiosciencereview.com/forum/index.php?threads/schiit-modius-balanced-dac-review.13769/