I sent this as a response to a private message on reddit's headphone group, but here's the best way I can describe ti:
It's really hard to describe the difference, but I'll try. From your iPhone to your MacBook to the Deckard's built-in DAC, those DAC chips sound pretty good. Sharp, detailed in the main instruments, vocals are clear, etc.
What multibit does, specifically Schiit's multibit, is really make each instrument have a 'place' and depth in the music. Do you want to focus on just the guitar in the left channel? Well it's over there and detailed enough that you can hear pretty much everything it's doing. The scraping of the strings, the tapping of the guitar body, its exact tone and attack. Music on other DACs just sounds closed-in and "digital" in comparison.
Did someone cough before the song started in the studio? You'll hear that level of detail too. The bass isn't just a "thump" -- each note is clearly enunciated, and it can hit your body in a way that's beyond just a 'bass bump'. It goes deeper. It's all presented in a very smooth, analog-sounding way that once you go back to other DACs you'll immediately noticing the lack of.
If you in any way can spend $600 on a DAC without it being a huge financial hit, I would recommend trying it. Or even buy the Bifrost Multibit to try it out and return it if it doesn't do what you want it to do -- it'll cost you $30 to try it out and send it back.
I was very happy with the Deckard, but once I read thoughts on the Bimby on audio sites my itch to try it grew and grew. I don't regret it at all -- in fact I sold the Bimby and got the Gumby. So yeah, I think it's worth it.