The spikes may not be needed at all. I once had my Thiels on hardwood - made no significant difference with or without the spikes (I spiked them on thick ceramic tile) in my room. The purpose of the spikes for Thiels, IMO, is more to couple the speakers to the floor over carpeting than vibration control. The Thiels are very very solid, so I don't think vibration is as big of an issue with them. In my opinion, I don't necessarily agree with "... I know I should be using them up on the spikes ...". Of course, your situation is most likely different than mine - my speakers are placed where the side and rear walls are not a significant factor.
