I've got a set of NX-Otica kits on order and plan on building the triple 12" OB subs as well. They will be in a room with travertine tile floors over slab. What have you all used for feet under the bases when placing them on hard floors? Bases directly on the floor, felt pads, spikes with cups, Herbie's dots, Herbie's Gilders, IsoAcoustics Gaia isolators?
If you've used something more exotic, like Herbie's Gliders or the Gaias, did you try them without these beforehand? If so, what differences did you find before and after?