No, do not under any circumstances send it back. They have a track record of taking months longer than expected to do upgrade work. I personally had this experience and it was agonizing. Ultimately Art felt bad about this and sold me a new one at maybe 60% of list, and returned my old one intact. The new one had the updated circuitry and yes it does sound more transparent, tighter, cleaner, BUT, the overall character of the sound is the same and if you are not comparing side by side you may or may not miss the improvements. My older unit is a 3A with continuous volume control and I found the "steps" too large on the new one so I sold the new one to a friend who loves it.
Bottom line: if you want the new one, sell your old one and buy a newer one.
Bottom line: if you want the new one, sell your old one and buy a newer one.