There is plenty of variety to be found in Kona, but for the most part I wouldn't call it all that advanced. I think you'll find that most companies "cater" to the open water diver simply because that's what the vast majority of the divers that get here are. Kona has a variety of sites, some will be reef oriented, some will be structure and topography oriented, some will be more critter oriented, many will have a mix of all. Most sites have deep water very near the boat mooring, however for the most part the reefs do tend to peter out to sand and boulders below 60'-80 feet or so, although there are excerptions. There are a few tech instructors around, one or two visit this board on occasion, that I think hitch rides with a local company or two, that may be of help for some serious "advanced" stuff. I"ve seen "advanced" dives touted as deep, dark or drift, in some cases, I suspect you can find those without paying for an "advanced" charter on occasion with several of the companies.
We're coming into the slowdown after easter, so there may be fewer specialty charters scheduled in advace with some companies that offer them simply becasue they need enough divers to make the specialty charter go. Check around, you may find that most of the companies are pretty similar in what they offer. Some are larger, some are smaller. In my case, I'm small, and sometimes it's tough to guarantee going out for just one customer... I go with just two (gotta get to two to get to 4 or 6 on the boat) if scheduled well in advance all the time, but one just doesn't make it work unless there are others on board, and when we're lightly loaded we can do some different stuff if the divers are up for it.
I don't think you'll find a bad dive up in the bunch here, everyone's pretty good, all are somewhat different from each other.