HD 660S2

Tubes do help the HD 800 S, it becomes more "HD 650-like" by adding some warmth and taking the edge off in the treble. Though it's a much "Softer" presentation than the HD 650 below 4kHz, as shown below. Though, the maintenance needed to upkeep tube amps can be annoying if you're used to solidstate.

I don't think the FiiO BTR17 has enough juice to drive the Sennheiser HD 660S2 since they're super power-hungry. That's exactly why I keep mine at home on a proper desktop setup. But if it sounds good to you, enjoy it, man!

Yup. In my experience, unless you have a pair of actually power-hungry headphones (and it's a short list!), you won't hear a big difference between a $9 dongle and a VERY expensive stack. The 660S2 isn't THAT hard to drive; even with a North American Apple dongle and an iPhone, I listen around 60% o

I’ll take almost anything over the 770, so … yeah, they’re both better than it. 😂 The 490 definitely has a better soundstage in terms of both width and separation within it; the 660s2 was a step up from the three blob people complain about with the rest of the 6X0s but it’s not as good as something