If you are I have a theory on that, first thing is James stopped using the Strategy400 power amps about a year and a half ago that he would run with his VH4 and started using the Mesa 2:90.
The reason the Strategy 400 is such a popular poweramp amongst audiophiles is because it does not color tone like other poweramps and has tons of headroom so that allows the VH4 to really shine.
Also Kirk's tone suffered when he started using those Randalls.