I don't know what you're used to sharpening, but if you haven't worked with S30V before, it can be "challenging" when you're first introduced to it. Ease of sharpening is not one of it's more attractive characteristics. OTOH... if you have a lot of experience with it and it's just this particular knife that's wooling you, then my guess, just from the info you've posted, is that your Casbah has a different bevel angle than the BM Worksharp you're using. All of the Worksharps that I've seen, both the BM branded ones and the Worksharp brand, are set at 20 deg. (+/- a little bit). That's the angle they list in their descriptions and directions.
Benchmade has gotten better with their factory bevels in the last couple of years. They're more evenly ground and their factory angles are more acute than they used to be. All of the Benchmades I've gotten new in the last couple of years are factory ground at a bit more acute angle than 20 degrees. In fact, I use my Sharpmaker at 15 dps to do my initial touchups, and most of my Benchmades have responded well to that angle setting.
So, as I said above, it may be that your Casbah was originally sharpened by Benchmade at a lower angle than the Worksharp's 20 deg setting. That means that you're creating a new bevel, sort of like a microbevel, at a steeper angle. That'll take more work than just matching the factory bevel angle for a quick touchup. The diamond side of the Worksharp is going to give you some noticeable toothiness to the edge. You may be feeling this and assuming it's sharp when it's really the toothiness that you're feeling.
The high-grit ceramic rods will polish this up a little, which is what they're supposed to do. Since, however, the edge is not really sharp, just toothy (like micro-serrations in a way), the polishing doesn't increase the sharpness. In fact, it makes the edge feel a bit more dull. High-grit ceramics, like strops, will refine an edge that's already sharp. They'll polish up that sharp edge and make it noticeably sharper. But they won't do that on an edge that isn't already sharp unless you spend a lot of time on them.
To see if this is what's happening, I'd suggest marking both sides of the bevel with a black Magic Marker. Then use the diamond plate on the Worksharp and take a few light strokes on each side of the blade. The area where the marker is removed is the area you're sharpening. If the marker comes off all along the bevel, not just on the very edge, then your Casbah does indeed have a 20 deg bevel. In that case, you probably need to add in an intermediate stone that's going to continue sharpening while also smoothing the edge some. Something like an orange DLT diamond stone (F for FINE) is probably a good choice. After you work with that some and the edge is sharp, you can move to the ceramic rods in the Worksharp.
If, however, the marker is removed at the top of the bevel but not down near the edge, then your Casbah is sharpened at a more obtuse (higher) angle than 20 deg. You'll need to raise the spine of the knife up some to lay the edge bevel flat against the diamond plate. You'll just have to experiment to see how much to raise it. USE LIGHT PRESSURE to find the correct angle, then try to hold that angle while you're sharpening. OTOH, if the marker is removed down at the very edge of the bevel (the apex) but not all the way to the top of the bevel, then your Casbah is sharpened at a more acute (lower) angle than 20 deg. and you're creating a microbevel with your sharpening. If you have a Sharpmaker, try using that at the 15 deg setting and see if you get better results.
