Audio Research Ref 6 vs 6SE

Would like to learn about the difference between ARC Ref 6 and 6 SE. Information in the web said that 6 SE involves upgrading 18 capacitors and 14 runs of wiring. And, owners of ARC Ref 6 can upgrade it to 6SE at a cost of $3,000.
How far is the actual difference in listening? Does it worth the money to upgrade? Would dealers in different parts of the world able to do the upgrade which seems to be done on site?