Floor standing speaker isolation advice needed.


I have an older pair of KEF Reference Model Twos that currently sit on their brass(?) feet on the floor. The floor is tile but not solid cement underneath. I bought two .5" thick granite tiles for underneath the speakers and am wondering if I need to do anything else like put the spikes on the brass feet, add sorbothane under the granite tiles and/or under the brass feet or something else I should be considering? Things sound good on the top end but seem a bit subdued/muddy in the bass region. The KEFs are being driven by a Parasound Halo A23 and I’ve got a HSU VTF-3 MK 2 helping out the bass, mostly for movie duty.


Thanks for any advice.
asahitoro
@ebm Your suggestions are very good. They're actually based on real experience. Keep them coming. Simply ignore geoffkait. Only the newbies don’t know that he’s Cliff from ’Cheers’.
Anyone (geoffkait?) think the IsoAcoustics Modular Aluminum Series stands will translate the same Performance as their smaller stands and footer devices???
Im thinking of trying them under Harbeth 40.2 (that I want lower than traditional stands for this speaker). The 40’s like the bottom to ‘resonate’ just like the rest of the cabinet and are getting good reports gently resting on top of the extended tenons on the TonTrager stands, so I’m wondering if the ‘rubber cups’ on the IsoAcoustics will kill some of the resonance that is making these speakers sing a bit more.  I know, Tough specific question here without trying... and no trial with the Modular Aluminum Series. Drat. 
I’m high on mass-on-spring isolation devices which have become ubiquitous. In the beginning there was Bright Star, Vibraplane, Townsend and yours truly. It’s like walking a tightrope or a razor blade trying to balance all the variables - internal damping, spring rate, number of directions of isolation and load capacity and of course cost. I eschew getting rubber but I suppose a little bit can’t hurt much, and too much slows things down too much. For myself I forego all rubber and almost all internal damping, preferring very hard cones, high carbon springs, high mass and extremely stiff boards.
@jriggy Whilst you may see improvement by trying out different stands with the Hatbeths don't forget that they are probably the most advanced speakers ever built when it comes to controlling resonances.

Everything from driver material, driver mounting, and panel resonances has been meticulously considered by the designer. In fact the designer, Alan Shaw once said that you could place them on a stack of telephone directories if you so wished and they would still sound good.

I'm sure he's right. I just wish all speakers were designed and built with such care.