Hey as a Schiit owner and Crack owner. I HIGHLY recommend skipping the Vali 2 and moving to the Crack. I've listened to the HD800 through both the Vali 2 ( Borrowed from a friend ) and the Lyr 2 extensively. Neither of these amps have what it takes to drive the HD800 well. Don't get me wrong. They are great amps, I use the Lyr2 with my HE560's at work all day and it drives them wonderfully. But in my experience the Vali and the Lyr leave the HD 800 sounding anemic. They lack bass, you will get the oft talked about sibilance, and the oft talked about veil.
For the HD800 I use either the HDVA 600 ( very expensive ) or the Crack ( which is on sale 249 right now). While they are in totally different classes, the sound profile in terms of EQ is very similar. I'm pretty sure if I'd have stuck with the Lyr 2 I'd have sold the HD800's - instead I bathe in their divinity.
Now I just gotta find somebody to loan me a Vallhalla 2 and a WA2.