Whats up man? Sounds like you have a couple of issues. First off I run my own Turf Managment and Design company out of Oceanside Long Island. I've had many situations needing my help and yours seems quite similar. Yourself being on lawnsite is unique to me, I'm glad that others closer to me have similar interests.
Seems like before you go out to Home Depot and spend a hundred bucks on lawn products that might or might not work, think twice and spend your money on a professional who you feel comfortable with. There are many Physical aspects of turf managment, as well as costly machienes to ensure results!
I can almost guarentee that the brown spots are not from grubs. This summer was considered to be the 2nd hottest summer witht he least rain. The sections are from burn, or scortch. If you would like, thatch the area's either with a rake or blade rake, use a weezle to open the patch's up, seed area's using zoysia seed, or buy plugs. I think there like 15 bucks for a small tray of plugs at retail nurseries. This should work... for the time being..
How large is your lawn? Have you ever considered eliminating the zoysia and growing beautiful grasses such as ryes, dwarf tall fescue, or bluegrass? Hope the info comes in handy.......