You can plug the HD800 into a quality laptop if you want and get good sound quality.
A 70usd FiiO Q1 will work a tad better, a 700usd Bifrost/Asgard2 a tad better than the FiiO and a 5k usd Auralic combo will sound a tad better than the Bf/Asg2 combo. But differences are subtle for the money invested once you've passed the Q1/E10K/Fulla.
That's not that important in the big scheme of things. What's important is whether you want a headphone like HD800 or not.
People who don't like HD800 as it is normally say HD800 is picky.
HD800 has neutralish bass with very little warmth, recessed upper midrange and raised treble in the 6kHz region.
So it's not very 'musical' or punchy without modding or EQing. And it's not a good match for a wide range of recordings.
You can EQ it, mod it, etc. You can pick a Porsche 911 and tweak it to be an off road vehicle, that's granted. But sometimes picking an off road vehicle in the first place is a much shorter path to the goal of having an off road vehicle.
My advice is to focus on what kind of sound you want, the more precise you can describe what you want, the more we'll be able to point you in the right direction. As
@Music Alchemist
suggested, you might like HE400i better than HD800 so keep that in mind.
If you want lean but tight bass, smoothened upper midrange, bright extended treble and wide stage then HD800 is the one to pick, if you want body in your bass, lively guitars and pianos, and relatively smooth treble then HD800 won't do that for you.
If you are willing to mod or EQ your headphones we have tons of variables to play with. First thing I suggest is trying to EQ the HE400i to your liking, then (if you still feel the need of getting a new headphone) find a headphone that measures like the EQed HE400i.