Awesome reply! So you actually sold the 4490 and the Lyr 2 in favor of the m9XX!? I'm going like the exact opposite route by now testing the multibit and Lyr 2. How was your experience going from the 4490/Lyr2 to the m9XX? I would love to hear it. What do you use the m9XX with? I'm guessing your 400i and the THX00?
Good explanation on the H10. What is an example of a balanced output DAC? Sounds like they're going to be over $1k though if the bifrost or m9XX are not even balanced. Do you need balanced lines from the headphones to take advantage of that? You would recommend the G109A over the Lyr 2?
"in favor" probably isn't a good way of putting my reasons for the switch. It had nothing to do with sound, but rather feature set and size. Sound wise, I loved the Lyr2 and 4490. However, I was basically never using it, because it had to stay on a desk at home, which I rarely get to listen to music that way these days. Most of my listening comes either at work or walking the dog, or at a starbucks, or walking around the house doing chores. So my 4490 -> Lyr2 -> HD650 setup was just being neglected. I use the m9XX with the HE400i and THX00 mostly, yes. But it works well with every headphone in my signature (you'll notice they're all very efficient headphones, everything I own can be driven well out of an iPhone).
I know the Gustard DAC that massdrop drops pretty frequently, the X12 is balanced and specifically designed to work well with the H10. https://www.massdrop.com/buy/gustard-dac-x12-usb-version It's under $500 right now. You don't need a balanced headphone, as the H10's output isn't balanced. People talk about balanced like it's all or nothing. Essentially the longer the signal stays separated, the better. With the X12 -> H10, the signal stays separated until the very end, right before your headphones. This is the best solution short of going fully balanced.
The 109A vs the Lyr2 is a total matter of preference. They're great amps. I'd probably get the Lyr2 though. Mostly comes down to your tube hybrid amp vs pure solid state amp preferences.