I had all three, so I'll post my thoughts. The irDAC could certainly be end-game. However the order in which I purchased these was:
- Gungnir Multibit
- Arcam irDAC
- Bifrost Multibit (upgraded from Uber)
As previously stated by multiple people, the Gungnir Multibit is an upgrade over both options 2 and 3. I already had it, which is why I sold both options 2 and 3.
My opinion is neither options 2 or 3 are better - just different. If you like the Schiit Multibit house sound (and obviously I do), go for the Bifrost. I personally found more depth and dynamics (and obviously I like this too) with the irDAC in my system, but note you will only notice this once you have a significantly resolving system (i.e. high end speakers/headphones and amplifier). Without a significantly resolving system, you may not even notice a difference between the Bifrost and Gungnir, as has also been previously reported. Of the 4 headphones I was using when I first purchased the Gungnir, on only one did I notice a significant difference in depth and dynamics. But you will likely notice what has been referred to as the smooth, analog nature (Schiit Multibit house sound) on the less expensive Bifrost.
TL;DR - Gungnir Multibit will be an upgrade over irDAC. And as it has been suggested, Yggdrasil gets you even more