I actually don't think the M3K is that bad of a source. It has low output impedance, a low noise floor. The only thing is that its amp is not the strongest, but I don't think the ER3s are that hard to drive anyway. Do look into the ER3SE and the ER2s if you are considering upgrading. I have read that the ER3XR is a bit muddy, and that the ER3SE is a better choice. The ER2s seem interesting too, with a dynamic driver setup.