Best way to "foot" a subwoofer ??

Kgveteran is essentially suggesting that you construct large bass traps over your concrete floor.
(a flexible, insulated wall or floor works much like a bass trap)
It's an excellent suggestion, if your room can accommodate it.

Here's a link to instructions and theory for building effective room-sized bass traps for very little cost.
http://www.ethanwiner.com/basstrap.html

Have you thought about a riser ? You could build one out of 2x4's and use OSB(oriented strand board) tongue and groove.Use a ton of liquid nail and screw the hell out of it with drywall screws.Wa-la,floating floor again.Thats how the big boys do it.Get some 2'x4'(4-5 inches thick should do)sheets of owens corning 703 board and cover it with some real porus fabric and kill those first reflections.Build a bunch of RPG skylines to diffuse the rest of the flat surface and you are on your way.Read,read,read.That room can work if you work on that room.

Kgveteran;

Yep, (2) of the walls are concrete, regrettably, I located my listening room in my basment for maximum "isolation", (3 kids, one patience-running-thin wife)but as "Snickelfritz" --(thanks!) so accurately points out (and as I again, regrettably found out) a concrete floor just doesn't assist the bass in any way.

Boy do I miss my "old" set up (former dwelling) with a good old fashioned "floating floor".

It's this apparent lack of bass-impact that drove me to purchase a sub.in the first place.

Same speaker, new "concrete floor" room, and it's like someone cut the bass balls off my speakers!

Thanks guys for your input. I'll just have to keep experimenting.

Concrete floor.It is very difficult to get that bass right on that concrete floor.Most of that room whomping bass starts with a wood floor on floor joists.Are the walls concrete ? Good luck my friend.

Generally speaking, spikes under a subwoofer are unnecessary, unless the enclosure is tall and/or unstable.
Rubber feet work better, and help reduce mechanical buzzing and resonances.

Room reflections and standing waves are usually the cause of flabby or "slow" bass.
"tight" bass is almost always the result of smooth, accurate in-room response, and has nothing whatsoever to do with the feet under the subwoofer.

This can be very difficult to achieve in some rooms.
For example, a perfectly cubical room made entirely of concrete would be the worse scenario, and would suffer from significant bass overhang at certain frequencies, due to overlapping standing wave patterns.
If your room dimensions are all different and not even multiples of each other, the standing wave distribution will be much better and the bass "tighter" and quicker.

Obtain an SPL meter and tripod from Radioshack, and a CD with 1/3 octave bass tones from Stereophile.
Measure from the listening position at ear height.
Depending on the size, shape and construction of your room, you may find that there is at least one really big peak/valley below 100hz(+/-6db is pretty typical, and some rooms are much worse).

Try to get it smooth; +/-3db or better should result in tight, realistic bass, depending on where the peak/valleys occur.
It may be necessary to move the listening position.