disastermouse
Headphoneus Supremus
It's also new years (and christmas) vacation time so it's just bad timing too.
I've used the xonar essence STX before, and I'd say the schiit stack is an improvement over that. You only need ultra on the magni if you want preamp functions (meaning line outs). I think there are other upgrades but that's the main difference. The ultras do have a nicer finish too. Look it up on their website. Or you could just consider consolidating your hp collection and sell them to get a better headphone.
Actually, Magni 2 Uber has more power too. Only need the Modi 2 Uber if you need the extra inputs.