I can’t see a problem in getting it within your fit window so long as the steerer has not been cut and the seat post is long enough, it won’t be optimal (toe overlap, steeper seat tube, narrower bars than you may want) but should be workable. Biggest thing may be handling.
Set the saddle as you normally would, height and setback. If you have no reference measures, set height so you can pedal backwards with heels on pedal, go as high as possible like that without heels losing contact with pedals or you needing to rock hips. If you run a traditional saddle I would set it at 6cm setback from nose to BB (8cm maybe on a short nose saddle).
Make sure saddle rails are within allowable range and seat post is not past minimum insert. Cannondales have high top tubes and long seatposts so you might fit this is easier than it might have been with a ‘compact’ framed bike like a Giant TCR.
For the front end, assuming an uncut steerer, I would try a 130mm stem at full height.
The frame reach does not differ that much 52 to 54 to 56 but stack increases, and running lots of spacers (which you would do on a 52 ) not only brings the bars up but also back, reducing reach. You may need say an extra 6cm of spacers which may lose you a few cm.
You might fit an even longer stem than you would expect to make up for the shortening, just beware the handling will slow to the extent the bike might feel a bit crap.
Just note Cannondale Si headsets don’t allow for spacers above the stem and you need the steerer tube to sit ~2mm below the top of the stem. You can at your own risk put spacers above the stem for fitting but it changes the support inside the steerer against being compressed by the stem.
If that all works I would try lifting hands off bars when riding hard, see if you fall forwards. If you do it might be too little saddle setback, too much reach or drop.
I am 5’10" and ran a 52 CAAD12 (same geo as old super-six) perfectly comfortably. 40cm bars, 110mm stem, 20mm spacers.
If this is a new supersix they are slightly shorter and taller but only by a few mm in a 52 (I think).