Speaker Stands adapters for Heavy Speakers?

I just bought a pair of GM Europa speakers. They are heavy (48 lbs) with a width and length of 8 x 10.5. I have sandfilled premier stands (paradigm). The stands are heavy enough but the tops measure only 7 x 9. I am concerned that I need a stand top that more closely matches the speaker size.

Does anyone make an adapter plate that can be used to adapt this speaker to the smaller top plate? Do you think Blu-tak is enough to secure them?

Thanks.