Do you know the reason why there is no option for both pickups to be engaged as humbuckers simultaneously?
first off congrats on wonderful gift - I have a 2001 standard 22 with Dragon II's and freakin love it.
The pickups used in conjuction with the 5 way rotary switch are out of phase with each other, to give the 5 various selections.
Using the Dragon II as a reference.
The bridge pickup is north side of magnet facing the screws
The neck pickup is south side of magnet facing the screws
combined with the clever design of the rotary switch you get the following settings
Position 10: Treble pickup
Position 9: Outside coils - deep and clear - parallel
Position 8: Inside coils - Warm version of the "in between the treble and middle pickups"- Series
Position 7: Inside coils - Crisp version of the "in between the treble and middle pickups" - Parallel
Position 6: Bass pickup
If the magnets were in phase with each other (like 99% of most humbuckers) you wouldn't get the middle 3 options - this is why if you want to use other makers pickups with the rotary switch one of the pickups (usually the neck) needs to have its magnet reversed 180 degrees making it out of phase with the other pickup.
if you tried to wire for both humbuckers on, they would be out of phase (giving the Peter Green mod) with both pickups selected.
like I said above I personally love the 5 way rotary, I have 3 PRS fitted with it.
2001 Standard 22
2006 CE24 Mahogany
I converted my old Santana SE into a pre-factory shape (Santana 22 / Goldern Eagle / Custom 22) homage using the 5 way rotary and and pair of Dragon II's
I don't miss the 2 humbuckers combined sound (I have other guitars for that) I really love the position 8 sound for rhythm work in a live setting.