Do you even read what I post?
I'll try one more time.
PCI-E card = Excellent SQ, headphone amp could have been more powerful, interference problems
Integrated = Decent SQ, worse headphone amp, no interference problems.
Youre getting solid advice from two respected members here...Perhaps you dont like what youre hearing them say,but it is still solid advice from guys who know their stuff.
I will toss my .02 into the fray as I have similar set-ups and products.
First I would dump the Beyer 990s.If youre dead-set against a valve amp then the 990 isnt a great choice.
I would go with either a Schiit stack and add in the Wyrd or their new(and apparently excellent)Eitr to help with the noise.Or you can try a Chord Mojo and ask Schiit if the Eitr is compatible.the Mojo is def warmer(and a better product IMO)than the Magni/Modi.
For headphones Id look into the Meze 99 Classic or HE-400s or 400i,or even a used HE-500(if you have good amping)...All are good choices for metal(metal is the majority of what I listen to).
FWIW I agree with your opinion of the X2s mids.