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I love the Raal SR1a with my EVO 400. The midrange is more meaty, "romantic," and the treble is tamed just enough, on the UL mode. If I am playing the SR1a for friends who are more treble-sensitive, I switch to the Triode mode, and the treble becomes *very* well-behaved while the rest of the strengths of the HP are retained, more or less. And on the May DAC - EVO 400 chain, I find that the SR1a has fuller bass.
Lastly, I enjoy the Sus on the EVO 400. I have relegated the Sus to laidback listening duty. With the EVO 400, the Sus becomes fuller, lusher, warmer, and perfect for days when I don't want to "rock out" or days I haven't slept well, lol.
@number1sixerfan is right. The Sus does play well with the EVO 400, especially if you are looking for some laidback enjoyment.