How to isolate turntable from footstep shake or vibration

You got that one right, there are an awful lot of factors that go into it, which is why I lean so heavily on educating on principles first and recommending specific solutions second. If I was there in person it would be pretty easy to eyeball and come up with a solution. Over email we have to fall back on generalities.  

Mass will solve most problems, if you can get enough of it. That's the trick. Fortunately mass is dirt cheap. Literally: one or two 50 lb bags of play sand, in a box several inches deep, put a piece of MDF or butcher block on top, you are pretty much golden. Put some Pods on top of that, turntable on Pods, now you definitely are golden.

You are doing it just like I did, Nobsound first as proof of concept, which then either is deemed "good enough" and you are done, or you like it and want more in which case Pods. If you do go to Pods remember Nobsound will work under all your other components, and you can make extra footers from the leftover springs. One of the all time great bargain tweaks.

"The most cost effective answer will be if the Oracle feet can be replaced with Townshend Pods." I disagree---that still amounts to adding springs to a turntable with a spring suspension.

And that is why I above suggested using a set of the Townshend Seismic Pods, not under the Oracle’s base (the non-floating frame which provides the table’s structure), but in place of the table’s stock suspension springs. Remove the Oracle’s springs, and install a set of three or four Pods under the floating sub-chassis---the bottom of each Pod resting on the shelf the table sits on, the top of each Pod in direct contact with the underside of the acrylic floating sub-chassis. That will isolate the sub-chassis from not only the shelf the table sits on, but also the table’s structural frame and it’s dustcover, as well as it's motor. In that regard, the Pods will provide an improvement in the sound of your table in general.

The Townshend Seismic Pods may be used thusly with any number of spring suspension tables; I have done exactly that with my VPI HW-19 Mk.5 (a Mk.4 with it’s stock platter and main bearing replaced with that from a TNT-5).

All this advice, all these springs, etc etc....way over thinking and too much work. Just put it on a dedicated wall shelf with a nice thick Butcher Block Acoustics slab for it to sit on, as I already advised. You could invite elephants into your home and your records will not skip a beat. Leave the design of the turtable alone! It is fine....isolate it, simple.

@esputnix, 

If you check with Oracle you will see where they have added a damping system to their sprung suspension -  Parts & Upgrades | oracle (oracle-audio.com)  MkVI Micro Vibration Stabilizer System (MVSS) upgrade; its a significant modification.  

What is likely happening is that the sub-woofer and foot-fall frequencies  are exciting a table spring resonance.  At resonance, an undamped system - in this case your floor - can amplify the vibration/displacement many times - often well over 20 dB.  So, every foot step causes the floor to effectively bounce causing the stand to bounce with it and the undamped table springs really bounce.  As has been suggested:

-a rumble/subsonic filter 'may' help because it may isolate the frequency that the subwoofer is producing that is exciting the floor from foot fall; example  Line Level Crossovers (hlabs.com).  There are pro/cons to these, but they are cheap and there are other types available - just search.

-modifying the table for the Oracle MVSS 'may' help because it now adds damping to the Oracle suspension that it currently does not have.  If it does not fix the problem, it may still benefit the table once the subwoofer/foot-fall/floor issue is resolved - but this is a significant mod that requires machining the base.

-mounting the table on the wall 'will' work; it isolates the table from the floor.

-adding a large mass under the table 'may' work.  

-adding subwoofer isolation feet or pad 'may' work because it may isolate the subwoofer from the floor enough so that the resonance is reduced or eliminated (shifts/isolates the problem frequency enough); and these are not expensive.  Examples are  Amazon.com: SVS SoundPath Subwoofer Isolation System, 4-Pack: Home Audio & Theater;  Amazon.com: IsoAcoustics Iso-200Sub Subwoofer Isolation Stand (Single) (New Model): Electronics;  Amazon.com: Auralex Acoustics SubDude-II Subwoofer Acoustic Isolation Platform, 1.75" x 15" x 15", v2: Musical Instruments.

-as has been stated - adding secondary springs under the table, is not generally recommended.  The phase relationship of the two spring systems can lead to very unpredictable results with resonances at different frequencies that can make the situation worse.  

Good Luck,