The Sti wheels are 53mm offset. how might that work out?
Depends on the spacer/adapter. The wheels you want to use are 53mm offset. If you use a 20mm thick spacer, you end up at 33mm total offset (53 - 20 = 33). If you use a 25mm thick spacer, you end up at 28mm total offset (53 - 25 = 28).
Now look at the pictures of wingman's car that are currently on the home page (He's SOTM this month). He has 17X7.5 wheels with a 40mm offset and they appear to be fairly close to being flush with the fender lips. If we added 0.5" to the outside of those wheels to make them 8" wide the offset would change to 33.65mm.
To put this in perspective, most of the 8" wheels on tire-rack's site are either 38 or 40mm offset.
You may be okay at 33mm, but it will be close. If I knew the offset of the stock 15X6 wheels, I could tell you with much more confidence. I definitely would not use an adapter/spacer any thicker than 20mm.