Neither of those are all-in-ones. Finding a powerful Amp is easy. Finding a powerful all-in-one (DAC + Amp) is a little harder.
I'm starting to fall in love with the DACMini anyway so it may all be moot. It's had just enough power so far and I can always boost the gain on it if I need to.
Really a good match for HE400s. It brings the mids forward and smooths out the highs. It's got good bass punch too. I'm really liking it... so much so, I think I'd pay the hundred bucks to get the Gain Upgrade if it proves not to get loud enough. So far it's been getting plenty loud. We'll see tonight after my wife and kids are in bed... That's the real test.
What you are talking about is the ODAC then. Its got tons of power, sounds awesome, and works great with the HE-400. If you bought it as separate component, you could also enjoy battery powered 'portability' with the amp.