Technically speaking I see the following differences:
- the housing / outer case made of aluminum is definitely better than plastic or free air;
- the inside transistors benefit of "free" heatsink due to the aluminum case;
- V7 has an increased bias current for the class-A output stage (thanks to the better cooling);
- the tiny PCB makes the V7 much smaller in height, the smallest op-amp made of discrete components I've ever seen.
Audible is very hard to tell without testing them in a specific device, but head-fiers state that the sound is crispier /detailed. Also, from what I've measured, I see that we can play slightly with the harmonics profile by mixing the V7 Vivid with V7 Classic, although golden ears might be needed to confirm the difference in their audio devices.
Bottom of line, the V7 Pro line is the best I've seen from Burson, and I've tested everything from V5 till now.