Or you could buy a pair of these.
Thanks for the suggestion, very useful to know.
However, I don't think these devices would work for my new speakers. I have just bought a pair of Russell K Red 150's and they do have a rather unusual spiking arrangement. The speakers sit on a fairly thin metal base plate which unusually contains the M10 threaded inserts but they are not located at each corner but instead are located half-way along each side.
The spikes are screwed down from the top and I have never before found it so easy to level each speaker. You simply adjust the front and rear spikes from above until the speaker is level front-to-back and then adjust the two side spikes until the speaker stops rocking sideways. Took me only a couple of minutes to level each speaker and get each one rock steady.
Under the circumstances I'm not sure how I could easily make use of any of the alternative feet options I've seen. I'm really impressed with this system. Check it out.