Heya,
I take it you want a neutral headphone with detail and good mids and a nice sound stage? That's the DT880. The M50 is not that at all. Avoid that thing. You'll eventually end up with a headphone like the DT880 regardless and it will be cheaper to avoid starting with entry stuff if you know you'll be willing to move on to the mid-tier already anyhow. Start mid-tier. You'll either love it, or you'll completely get out of hifi in general if you are not satisfied and feel like your money was not well spent (in which case, that stuff will re-sale very nicely it does not lose value if you take care of it much).
If you want to make your experience decent without a lot of expense, keep it simple, go FiiO.
E7 + E9 + DT880
Or, Matrix CUBE + DT880
Or, Maverick TubeMagic D1 + DT880
Or, Asus STX or Titanium HD + DT880
Or, Asus Xonar + DT880
If nothing else, buy as much headphone as you can with your money. Spend less on source for now. Get a good headphone first. This will be most appreciable use of your money at first. The HRT MS2 + LDMK3 is a good setup. But it's also limited due to USB to what you can use it with. Plus, I imagine your music is in lossless or minimum 320kbps well compressed formats? It needs to be. So make that a priority if it is not.
If budget is in mind and you're using a computer, I would do:
Beyer DT880 PRO with Titanium HD
(total $360). It covers gaming, movies, and music listening.
If you want to be free of the computer potentially, then look at the above Maverick, Matrix & FIIO.
I suggested the DT880 PRO because it's virtually the same as the premium and saves you money. Alternatively get the DT990 PRO if you want more bass, or the DT770 PRO if you want isolation/privacy. The DT880 is neutral.
Other headphones to consider (neutral, based on your DT880 choice): AKG K702 &Fishcer Audio FA-002
Very best,