I have had a chance to compare the two side by side in my system. I have owned a V-31SE for about a year and had the VK-51SE for 2 days courtesy of my friend. The VK-51SE sounded like it had a slightly more deeper, articulate bass over what is already very impressive in the VK-31SE. In terms of transparency and "air", yes a tiny amount as well. Truth be told, it was not a night or day difference, they are very close to my ears. If your system has the ability to resolve the slightest differences, maybe the difference in price would be worth it, otherwise spend the difference elsewhere in the system.
