I have the Helicon 800's which are very similar to the MS5's, and I have found a nice "synergy" using Synergistic Research cables. These seem to add some additional depth and accuracy to the soundstage and they make several different cable types to taior to your desired sound. I am using the Signature 10 X2's and I like them very much.
FWIW I have also found a tube pre is the way to go with most speakers. I have an Aesthetix Janus and I think you would be hard pressed to find anything objectionable about it even if you normally like solid state preamps. I am not familiar with your amps, but the Sony is known to be less than forgiving, so a tube pre may help depending on the balance you are trying to achieve.
FWIW I have also found a tube pre is the way to go with most speakers. I have an Aesthetix Janus and I think you would be hard pressed to find anything objectionable about it even if you normally like solid state preamps. I am not familiar with your amps, but the Sony is known to be less than forgiving, so a tube pre may help depending on the balance you are trying to achieve.