Get the outboard preamp. It will deliver the Sadowsky tone. That said, the Fender is not a Sadowsky, and a true Sadowsky partisan will notice the difference.
I'd get a Sadowsky preamp/DI box. Then you can still have a "Fender" sound and a "Quasi-Sadowsky" tone as well. I am debating this as well.
Considering that Sadowsky cut his teeth on hot rodding fenders for the studio, it depends on what one means by 'sadowsky' tone. I'd say get the preamp and upgrade your controls if you're looking for more tone shaping.
Thats what I did. Installed the VTC controls and Sadowsky J humbuckers. Only mod would be to remove the Sadowsky pup coils from their shells and put them into the Fender shells. Use a 1/4" drill bit and widen the end shell holes to accomodate the poles. No biggie. They will line up right under the strings. Then use the foam under your Fender pups to support the Sadowskys. You will have to cut them down a little so the new pups wont sit to high. Make sure the neck and bridge pups are in the proper shells. Screw em' in and adjust the pup height. Sounds like allot but it's fairly simple. The VTC controls have a very easy to follow diagram. If you wish, at that time you can shield the cavities via copper or shielding paint from Stew-Mac. Now for the sound? Very very much improved over the Fender kit and has Sadowsky-like tones. If you have played a Sadowsky with this set up then you have something to compare it to. Mine has the humbuckers, you can choose the single coil type if so desired. Does this make it a Sadowsky? No, it's still a Fender with another manufacturers electronics. I happen to really like the way mine sounds now.