Do you know how to?

I had a similar problem with an amp I owned and while this solution might seem like overkill, it worked.

I drilled a small hole in the center of the plastic cap and screwed in an appropriately-sized 'Easy Out' until it had enough grip that I could pull the plug straight out.

You should be able to buy a single Easy Out at any hardware store for a couple of dollars, along with the drill bit to match it.

Thanks Sfar, there has to be a simple and easier way to remove these plastic dust caps. I have a metal dental round hook that dentists use, I may poke a hole on the dust cap, insert it in and fish it out. Wacha think?
On my Focal speakers, I removed the dust caps with me finger nails, but these are, again, totally flushed inside the spkr coonectors...
Grrr, didn't think it could be this frustrated.
Tom6897, I too wish Agon would have a section for us to post pics.

Sure, if you have a dental hook that could work well but I still would consider drilling a hole rather than poking one through the plastic, you're going to want the hole to be big enough that the curve of the hook can get through and get some purchase on the back of the cap.

If you can get the hook in there and it still won't budge you might try putting a drop of rubbing alcohol at the edge of the plastic cap to help lubricate it. I've used it to help with a tight fit on plastic and rubber motorcycle parts because it helps sticky things slide but dries quickly and leaves no residue.

Dental pick, or drill a small hole and run a sheet metal screw into it. Grab the screw with your pliers.

Thread a small screw in few turns and pull. Also, you can pry them out with a needle. Doesn't matter if you ruin them as they will never go back in. They should come out very easily.