I recently purchased a SoundCraft Spirit M4 off of ebay so that I might simultaneously monitor my computer audio (M-Audio Delta 1010) and a digital piano (Kawai MP8) with a pair of Sennheiser HD595's. The digital piano however when routed through the mixer sounds terrible. It becomes vague and muddied as opposed to the pianos onboard headphone output which sounds great. This despite trying every 1/4" and RCA input the mixer has to offer and adjusting EQ's accordingly. As an example. the rhodes voice on the piano does this stereo phasing thing where the audio shifts quickly between the L and R channels giving this neat wavering effect but which is barely noticeable when routed through the mixer. Has anyone suggestions? Regards.