Hi ctviggen,
I have a pair of HD650 driven by a Bottlehead Crack.
I've used it for more than a year and no problem with the tubes and or electronics.
The headphone amplifier is a kit,
but at Bottlehead they have someone that can put it together for you.
It's not small like the ones you mentionned, but that a plus,
more room for the components to have air to cool down.
Guy 13