Thank you arcticears. That's a great suggestion using the L7. I'm going to order one today. And thanks for clarifying the question of serial amps and gain vs. volume. I feel I'm sailing in calm waters now!

Thank you all for your replies, I very much appreciate your help. @arcticangel and @purpleangel I took your advice and just connected the Fiio E17 and this has worked very well and I'm really enjoying how it sounds. @arcticangel, I thought having the amps in series was not right but I felt the...

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...