A combination plate has a different grit surface on each side. DMT combi plates are available from any number of places, including Amazon.
You won't get any particular benefit from using diamond plates to sharpen Wusties or other similar knives, other than that they're fast and relatively easy to maintain. But good diamond plates are expensive, and diamond finished edges are extremely toothy.
I don't care for DMT plates. They're expensive to begin with, and end up being even more so because they wear too quickly. The plates with the interrupted surface tend to catch tips. The really good sharpeners I know who do use diamond plates for sharpening (as opposed to flattening), use Atoma -- which are absurdly expensive.
Sharpening Wusthofs and similar knives does not require super-duper stones. You can do a good job with good oil stones, or with mid-quality water stones.
My preferred set for sharpening those sorts of alloys consists of:
- Norton Coarse India (thinning and repair only);
- Norton Fine India (drawing the first burr);
- Hall's Soft Arkansas (refining and chasing the burr); and
- Hall's Surgical Black Arkansas (finishing).
Of course there are a great many oil-stone (or oil-stone types) which will do an excellent job. For instance, "Razor Edge" stones are better quality (but slightly more expensive) than the already very high quality Norton Indias; and while Arks give me the longest lasting edge for softer steels there are plenty of stones -- like "coticules" which I don't know well enough to judge.
You never want to put too much polish on alloys with fairly low scratch hardness, but you do want the edges fine enough to feel good in the cut and be long lasting. When you're choosing your final finish, stop and consider your steeling equipment and technique. It doesn't make a lot of sense to fully polish out an edge today if you're going to scuff it up on a rod the first time you take it out of the block, tomorrow.