I'm using a MacBook Pro connected to a Fiio E17 via USB and from there to a HeadRoom Micro Amp out to the K550's.
With gain set to 0 on the Fiio and medium on the HeadRoom I have to turn the volume up high on iTunes, the Fiio and the HeadRoom to get a reasonable and engaging sound.
Previously I was using IEM UE10's with the same amp/DAC combo and low to mid volumes produced a loud volume.
I've discovered that turning the gain to high on the HeadRoom makes the volume on the K550's really loud and the music becomes much more alive as opposed to seeming slightly far away and less engaging.
Not really understanding what gain is I've tried to read up about it but have been defeated by the more technical explanations. What I did read was that a 32 ohm headphone doesn't benefit from an amplifier and that using high gain can overpower headphones in this class. Now I'm wondering if I shouldn't be using these amps with the K550's. Does anyone have any advice around this question please?