I will echo what others have said. You can't go wrong with any Schiit combination: every piece is strong, musical, and a terrific bargain. I have HD580s and they're a terrific bargain, but oddly (for this forum) I listen to speakers almost exclusively. But I have a lot of experience with Schiit. I did all the upgrades on the Bifrost through the Bimby, which I gave as a present to a musically fanatic relative. The Bimby is an insanely great DAC! I would have kept it but have a balanced system, so will try a Gumby or Yggy. And I just got a Modi MB for a friend. Having designed and built gear for a long time, and swimming in high-end sound for 30 years, I can say the accomplishments of Mike and Jason in building great, reliable gear with such low prices is without equal.
Given that you want to have an affordable but versatile reference system, you really ought to go with the best you can afford. The Jotenheim/Mimby combo is $650. And you'll have all the power you need for any headphone, which isn't quite the case with the Magni. Well, the Magni 2 Uber is very powerful and will run anything, but the Joty will run any HP to its very limit. And you'll have a *world-class* balanced preamp too. But if you do go with the smaller separates, I urge you to get the most versatile of them, the Magni 2 Uber and the Mimby. If you ever replace them, their versatility makes them *far* more valuable as a backup, second system, or for resale.