I'll step in on the digital side. I've got a pair of the Sennheiser HD800S headphones, which I enjoy with the Mainline and the Crack-a-two-a (C2A). In fact, the C2A has become my new favorite with the 800S. If, going forward, you see yourself wanting to drive headphones of lower impedance, go with the Mainline. With regard to digital, I'm feeding the amps with the Benchmark DAC3-DX, which is an extremely capable performer. As a plus, it's got a nice SS headphone amp, should you feel the need for some of that SS punch. If you don't want to spend quite as much, consider the Schiit Bitfrost Multibit.
Best,
Joe.