Ironically, street tread isn't bad for sand at all. I'd guess best in order are balloon tires, dedicated sand tires, well worn street tires, normal street tires. You want a lot of contact area for float. The only problem with the stock 19" wheels is you have damn near no sidewall when you air down. Best hope not to hit buried rocks!
I see guys with RRS' running 20"-22" tires in sand all the time. Talk about no sidewall, but they do fine.