I don't think these phones really 'warm up'. It's more likely your ears getting attuned to their sound.I'm personally not a fan of tubes so my exposure is almost all transistors. Speaker amps will definitely have the power to drive these but be wary of the background hiss they tend to exhibit. This (and the space taken) are quite the reason I do not use my Cyrus integrated amp with my phones.
3/11/14 at 2:45pm