At least initially, I would go for the Blue Jeans Cable balanced IC. It is pretty inexpensive, made very well, and they have very quick service. Just to be clear, I now have and have had much more expensive cables. I can tell you that, if they have any effect (difference) at all, the majority of high priced cables really color the sound at best, or even mess with the timing and phasing at worst. And sometimes, they just sound good.
People start with colored components (which is ok, sometimes even preferrable), and then must find cables which allow an overall sound they like. Sometimes, the search never ends. It is just my opinion on these, but I believe the BLue Jeans are good enough to let you hear the system. If it is still bright (or too harsh, or too light, etc.), the issue is likely somewhere else (and it is not the 400xi). Good luck whatever you choose.