Heya, The Vali will handle the HE400 nicely. It will frankly handle almost all headphones just fine except for a few very insensitive ones. Whether I like the HD650 or not, well, doesn't really matter :) Very best,
Without amplification? It will run, contrary to tons of belief. I've ran it from a cellphone. It's better with an amp. But I think there's a lot of misinformation that this headphone needs serious power to do well. The Fiio E10 seems to power it just fine to my ears, let alone something more powerful (yes it sounds a little different with higher powered sources, but I think it's overstated that it's necessary to sound good).
What are you looking to have different? The O2 covers your solid state needs. Everything in the $400 and under area is mostly just going to be a different flavor, but not really make anything "better" beyond simply giving you another flavor to taste to expand your preferences.
If you really wanted to branch out, try a tube. The new Schiit Vali would be more an attractive option than the Asgard at this point since you already have the O2. Alternatively in the...
Heya, 300ohms - 260mW (Magni)300ohms - 220mW (Vali) For reference, the Little Dot MK III tube amp does 350mW at 300ohms. It would not be underpowered. It's nearly the same as the Magni. But with tubes. Very best,
The M50 doesn't need an amplifier, at all. So with your budget, I would focus more on how you split the signal from the phono pre-amp to a suitable device that outputs to a headphone and/or speakers. You shouldn't need another amp with pre-amp ability just to output to a receiver for speakers. Using a receiver at all in this setup defeats the point of even using an analog vinyl setup in the first place. I would look for a phono pre-amp that has a headphone port...
It's a market thing. It used to go on sale often. These days I'm seeing more market deals on the 250ohm version of the DT770 and the latest released of the Limited Edition 32ohm really changed a lot of people going for it instead of the 80ohm because of the less need of an additional amplifier to really push it for portable and simple devices. Add to that the floor of closed headphones that were released this past year or so, that also land in the $200ish area,...
The Vali's max output is 660 mW. It will power it enough for listening.But per Dr Fang, the HE500 is suggested by him to have about 1 watt (1,000mW) for full dynamics. More appropriate for the HE400. Very best,