I have the EF2A with stock tubes and I really have no complaints with it. It fills in a lot of bass for the HE-400 and gives it a very warm, musical quality. It also makes a massive difference for my Denon Ahd-2000s. My brother is in the market for an amp though and I have some spare spending money so I'm considering taking the opportunity to upgrade. Would the Lyr provided a significant and worthwhile upgrade for the HE-400s or would I need a more expensive headphone to really benefit from the amp? I'm not planning on buying any more headphones for at least a few years since I love the HE-400s so much, except maybe a T50P as a modding project.
Also, would the Modi be a suitable DAC for it? I'm noticing that the Bifrost costs 4 times as much, can a DAC really make that much of a difference to justify that cost difference?