I better chime in here, I owned a Line 3 running it on NOS tubes for the outputs....had it about 3 years, liked it enough to trade in on the 3SE, and I HEARD improvements in every area......and believe me I knew the Line 3 well, lots of hours......IMO the 3SE is in another league. You need to have good enough associated equipment to hear the difference.
I didn't realize SF was offering Preamp upgrades? I was waiting for the announced upgrade of the Processor 3, which never happened when the company was purchased.
IMO SF preamps represent a good value.