Spikes for very heavy speakers

only where the equipment rests is bare floor..... rest is carpeted.....I know....I know... this would be some crazy echo chamber if it was all concrete

Audio Points may be an option here. There are a set that can handle upto 450lbs and you can add the coupling disks or APC-D4 invert to protect the spikes from bending. I should add they also make significant improvement to the sound.   Good luck

I think you also have to take into account 215/4= 53lb is aprox what each spike see's (speakers are not evenly weight distributed) not really too much when you look at it like that. 

If it were me I'd get some ISO acoustic footers for your speakers they do wonders I'm my system and they are not that expensive. Just get the ones for your speaker weight as they will need to support that 53lb each. 

If your really concerned and want to go very cheep go to a local machine shop and get them to turn off some metal discs (brass for example) with a dimple in them for under your spikes. that's the lest expensive way to get floor protection. 

I never understood why people here never think to use here local machinist for many of our simpler metal work.  most seem to want to buy some expensive thing with a fancy name, made in another country then use a local shop to make the same thing or better for 1/4 the cost.

In addition to the concerns expressed around using spikes, you may also want to consider some options which allows for an easi(er) mechanism to move them around to better optimize their placement. A friend of mine is utilizing small wheels under his Wilsons on his ceramic tile-over-concrete basement floor with no discernible negative impact on the sound quality.

Since I will be placing them in my basement which has concrete slab ....should I first get a small piece of thick solid wood...say 1inch think and place them on such a wooden platform or do you think it is OK to have the spikes direct on the concrete....

Straight into the concrete slab, the best way.
Adjust the spikes so there's absolutely no back and forward "even minuscule" rocking.

Cheers George