Bifrost 2/64 hits harder, has tighter/more extended bass, has more air/extension in the treble, and has a deeper stage than the modi multibit 2. The MMB2, however, seems to have a smoother mids-treble transition that isn't as "harsh", and overall feels like an easier overall listening experience. Tonality wise they are more similar than different, with the 2/64 being maybe more "U"-shaped as the extension on both ends is more audible.
I think the Bifrost 2/64 is worth the asking price, and the modi multibit 2 is also worth the asking price value-wise. The 2/64 is clearly better than the modi multibit 2 technically when a/b-ing, but in the end I think I'm probably going to sell the 2/64 and keep the MMB2 as it makes a cleaner stack with the piety. Ultimately, the modi multibit 2 crosses my baseline for "engagement factor, clarity, and resolution", whereas the original modi multibit 1 was too muddy, blurred, and warm for me, and that makes it good enough for me for the longrun.
upstream: macbook air m2
downstream: piety, JAR800