Of course it's not the best pairing, but OP has a price point he's shopping within and your one opinion alone doesn't hold much value. Neither does mine honestly! Not saying the ATOM is better than what's listed there but it's one acceptable option and for the HD 800 there are many! But most important is what
@Wifiman is willing to spend and what he ultimately wants
Here is some one who has heard this pairing!!! So based on my experience with solid states and the HD 800 and his experience then it's more helpful to maybe suggest Wifiman be prepared for a less than stellar performance.
Still the appeal is how clean the output is, lots of clean power but that's not really useful unless your driving like an HE 6 ect...
As far as solid states go the VERY best I've heard thus far is the new Bricasti M3 fully differential DAC AMP the new Benchmark system is also exceptional for different reasons. But again if Wifiman want's to stay around $400ish those impressions are of no use to him
But until he has heard it this is all speculation! That said, I again don't think he has much to worry over. Even if the pairing is less then stellar, it'll be easy to sell or trade to another user here or else where!