Hi, I can't answer this directly. But I did go from a VK 60 to a VK75SE. This was several years ago.
The VK 60, using the same 6sn7 input stage as the VK75 has a warmer tonal balance.
The VK75SE has a newer and dedicated power supply for the input section, now based on the 6h30 tube. In my system, this amp was much more extended on the extremes, particularly better bass control, depth and definition. Also more quiet background allowing a better (wider deeper) soundstage and quite a bit better detail retrieval. However, tonally the amp is cooler, loosing some of the warmth.
All this said, both are great, really system matching is the important item...
The VK 60, using the same 6sn7 input stage as the VK75 has a warmer tonal balance.
The VK75SE has a newer and dedicated power supply for the input section, now based on the 6h30 tube. In my system, this amp was much more extended on the extremes, particularly better bass control, depth and definition. Also more quiet background allowing a better (wider deeper) soundstage and quite a bit better detail retrieval. However, tonally the amp is cooler, loosing some of the warmth.
All this said, both are great, really system matching is the important item...