I personally think the Audioquest are adequate. I also doubt if there would be any significant difference using XLR's unless the Marantz gear was truely balanced and I don't think it is. Or, it could be beneficial if you had a long distance between amp and preamp. I hate giving this answer but it's the truth, the only way to know if you can improve on the King Cobra is to try a step up to see if a difference and if it's worth the extra expense.