Spike upgrade for Thiel 3.5's

I have the factory suppiled spikes but Im tweaking my system.
Im wondering what a good cone (or spike) would be to use to improve the performance of the 3.5's.
Im looking to tighter bass and better all around sound.BTW they sound great now,but as I mentioned Im doing some tweaking to my system.
Im 'kinda' leaning toward BRD cones but would appreciate any other ideas.I only need 6 cones/spikes.
My floor is a quite solid,wood suspended with thick pad and carpet.
Thanks!