Hi Sanders
Firstly i would consider the safety aspects, especially if you have kids. Plate glass (4mm/6mm can break easily and cause some very nasty injuries)
If its against a solid top then I would still make sure it was 6mm plate glass with polished edges (for obvious reasons) i have a pine unit with a peice of "anti-sun bronze" 6mm plate custom made at a glass and glazing place.............it cost £25
The glass in the link is tempered (toughened) so it would be ok in supporting an amp on a solid surface, but if its not then I would go for laminated as it does not explode into small peices if you catch the edge.
In short I would have a peice custom made in 6mm laminated in bronze.