Dave,
There is a marble and granite wholesaler in Lancaster. For granite, you will speed $50 a plate (custom cut). I won't worry so much about the added height unless your couch sags. I did talk to Audiopoints last week about using their Sistrum Platform on a granite slab with wood/carpet as flooring. They recommended against it because of resonance transfer back to the speaker. They did recommend installing 3/4" dia stainless steel or brass rods across the support beams with washers and nuts (2 - 4" beyond the speaker perimeter) to enhance structural integredity of your flooring and resonance conduction to ground. Email me if you need more info. For me, if you can buy 3 - 4 plates of marble at Home Depot and try spiking the speaker to the marble you would only be out ($2.50 x 8) and then you could experiment with the rods.
There is a marble and granite wholesaler in Lancaster. For granite, you will speed $50 a plate (custom cut). I won't worry so much about the added height unless your couch sags. I did talk to Audiopoints last week about using their Sistrum Platform on a granite slab with wood/carpet as flooring. They recommended against it because of resonance transfer back to the speaker. They did recommend installing 3/4" dia stainless steel or brass rods across the support beams with washers and nuts (2 - 4" beyond the speaker perimeter) to enhance structural integredity of your flooring and resonance conduction to ground. Email me if you need more info. For me, if you can buy 3 - 4 plates of marble at Home Depot and try spiking the speaker to the marble you would only be out ($2.50 x 8) and then you could experiment with the rods.