Thank you everyone for you help. I maybe should have clarified in more detail what I'll use the equipment for. I'll mostly use it for music and movies, and some for casual gaming. I have one pair of computer speakers (Bose Companion 20) and another pair (Logitech Z623) that are in front of the TV (I watch all of my movies from the computer that's connected to my TV). So the source of the sound will always be from my computer. The headphones will be used when I watch movies/TV-series/gaming alone and when I'm listening to music while working/studying.
Also, I've tried to figure out if a sound card is needed if I have an external DAC. From what I've understood from this thread and other sources a sound card is not needed if I only listen to music and have an external DAC but is good to have if I also watch movies/for gaming? Please correct me if I'm wrong.
The Aasgard seem interesting! This would be a bit over my budget, but how about Xonar DX + Aasgard + one of the DAC you recommended?
Otherwise, as some have written maybe I should just get the STX and settle for that now and upgrade later. This was harder than I thought it would be :p
As an Essence STX owner, I would like to think it would be enough for the HD650 & Bose.
With the Xonar DX connected to the Asgard, your covered, no need for adding a separate DAC, at least for headphone use
The Xonar DX comes with the XS4398 DAC chip already, that a good value for use with the Asgard.
And I would assume the Asgard is a better headphone amplifier then the Essence STX (& ST).
But to use the speakers with this setup, an S/PDIF optical input and analog output DAC would need to be connected to the Xonar DX's optical output.
There are some low cost ones on eBay, Fiio makes one for under $30, D3 or D5?