Ditto David12. When I asked, ARC was somewhat tongue-in-cheek about the circuit changes and parts that go into the SE upgrade.
Having said that, I doubt that ARC would charge $5000 to do an SE upgrade to my Ref 150, where the retail price of the tubes (8 KT150s 4 6H30s) being approx. $1800 and the balance (or, $3200) relating to snake oil.
OTOH, all that being said, ARC has at times described certain improvements or new models as "being in another league" or "in a different class" and so forth. That has not been my personal experience in a number of cases (e.g., Ref 3 to Ref 5 (not SE); PH-7 to PH8). Just my opinion.
So I am waiting to read comments from Carey and Oregonpapa.
BIF