I'm not a big fan of greensand because it is so incredibly slow to release anything and in such small amounts.
If you really want to use the fertilizers, which is fine, Muriate of potash (aka potassium chloride) and sulphate of potash (aka potassium sulfate), are super duper soluble and anything you apply now will probably be gone by next spring, so I would hold off until then.

Muriate of potash is a little cheaper than potassium sulfate and you also get more potassium pound for pound. But, you would want to make sure that your regular irrigations include a small leaching fraction in addition to the amount of water that the plants require to leach chloride out of the root zone since an excess can lead to burning and decrease growth/production. Sulfate isn't as big a deal as chloride.

Now if it were me, I would just put down a couple of inches of that compost next spring and till it down to 6 or 8 inches. Assuming it's a greenwaste compost, it will have a good amount of immediately available potassium and will be likely to provide plenty of potassium as it breaks down. I know lots of folks will say that compost is not a fertilizer but if you put down a 2 inch layer of a good greenwaste composte, it will give you a few pounds of immediately available potassium per 1000 sq. ft. right off the bat and provide at least another 10 lbs. over time as it breaks down.

In the unlikely even that potassium deficiency looks like a problem after you start growing next spring, then you can supplement with one of the fertilizers.

Eat a LOT of bananas, compost the peels and use the compost. Voila. :-]

I'm on a roll today!

I can't till it down because there are too many plants, roses, clematis that are already in the bed. Top dressing is the only way I can do it.

Top dressing would be okay. The immediately available potassium is water soluble K2O (that's why it's immediately available to plants) and should move into the soil easily with irrigations. That is, unless you're running drip under the compost. We can deal with that if we need to. As far as potassium for the long haul, it will move down slowly as the compost decomposes and you should be fine.

Eat a LOT of bananas, compost the peels and use the compost. Voila. :-]

Or that. :P

Wood-ash is another quick source of soluble K, so best applied in early spring.

kentstar, while wood ash is a great source of K, I can't use it as my ph is fairly high and wood ashes are very alkaline.
If your ph is low and wood's burned in your area, ashes sound good!

Urine has a lot of potassium.

Are you suggesting the OP pee in his/her garden?

It's been known to happen, hairmetal. :-D

Here is a link that might be useful: Fertilizing with Urine Threads

Greensand may be a source of Potash in the future, providing there is adequate levels of organic matter in the soil to give the Soil Food Web someting to live on so they can convert what is in that Greensand into something your plants can use.
You probably would need a lot of urine to get enough potash to your plants and that may take a long time, especially if there is not a functioning Soil Food Web to convert the potatassium into somethign the plants could use.
Your soil test should have had recommendations to correct that K deficiency, or your local office of the Ohio State University Cooperative Extension Service should be able to tell you what and how much.

If you have dogs that pee in your garden is that not just as good?