I would keep the C49 and cancel the Quad order by working with your credit card company by opening a dispute. They usually get things resolved quickly the one time I had to go that path. If it has not shipped from the vendor you purchased it from, there should be no issue with canceling the order.
If for some reason you have to take possession, sell it as a new-in-box, sealed, and never opened. I am not sure how a warranty transfer would work in that situation.
As mentioned above, the Benchmark LA4 is a great preamp at a reasonable price. I regret selling mine. I was not a fan of its wonky touchscreen controls, preferring knobs and buttons.
Good luck