So if you are looking to mash with 11.5qts then you have decided on 1.25/qt per gallon.
You need to figure out how much water your grain will absorb. That will be approximately .11 gallon/lb grain. So 9.25 x .11 = 1.0175. Call it an even gallon. (4 qts) So you should expect to collect right about 7.5 qts of run off from your mash.
Next we know you want 5.5 gallons at the end of boil, but you need to know your boil off rate per hour, and how long you are going to boil for. Most will lose somewhere in the 1.25 to 1.75 gallons per hour during boil, although this number can fluctuate based on humididty, how hard you boil, diameter of your boil pot, wind conditions etc. If we assume you will lose about 1.5 gallons during boil and we know you want 5.5 gallons into the fermentor, then you want 7 gallons pre-boil, or 28 qts.
We take 28 qts
Subtract 7.5 qts runoff from mash
= 20.5 qts for sparge. (absorption during mash is minimal as the grain is already saturated)
You can either do one big sparge at 20.5 qts, or two smaller sparges. For most one big sparge is easier takes less time, and will rinse your grains just fine.
PS. You may want to mash a tad thinner for a wheat beer mash, especially if you have typical sticky adjuncts, and add some rice hulls. So maybe consider 1.3 to 1.5 qts/lb