I have two pairs of 750's (one is for sale, I gave up on active biamping), one pair is modified to accept third party power cords, the other is not modified. Both pairs were re-capped. For both pairs high quality XLR interconnects sound MUCH better than any CAST I have tried (including the Nordost that you have).
Also, the Kubala Elation (single run, not biwire), speakear cables are MUCH better than the Kubala Emotion.
If you can, also try to compare in your system the Krell Phantom (top of the line, two box), to the Krell 202. The Phantom has a better, larger power supply and sounds better.