Hey Techno Kid,
I have the Asgard 1 (has the same power output as the asgard 2), and i can tell you it does a wonderfull job on the HE-400 coming from my Fiio E17.
If you are aiming for an upgrade later on like the HE-500, the asgard is about 95% enought for the HE-500.
In theory, the Asgard will pull 1 Watt to those orthos, and thats the power requirement for the HE-500 (for the HE-400 its less, but not really sure how much less).
If you can affor the LYR, it would be more future proof, but note that The Valhala has NOT enought power to run the orthos ( tried the valhala myself, sounded worse than my fiio E17, less power, less detail, etc.)
Personally i will keep the Asgard and go for the HE-500 or an Sennheiser HD600 later on the road, and add a DAC probably like the Bifrost. But thats for LATER.
So, for more future proof, LYR, for jsut HE-400, HE-500, if on a budget, Asgard 2. At least thats what i would do.... nah who am i kidding, id probably get the Lyr anyway LOL.
Some people say the HE-500 is too much for the asgard (cant say yet since i havent tried it, but i plan to as soon as my local shop has the HE-500 delivered, so i might comment then on the matter).