The Samsung rear speakers weigh 8kg each and these Harma holders can carry 5kg each.

According to our product experts :

This stand is equipped with plates

6.5 cm x 6.5 cm
8 cm x 8 cm
11.5 cm x 11.5 cm

so the biggest one is the nearest match to size of the rear speaker

Rear speaker depth 141 mm
Rear speaker height 203 mm
Rear speaker width 125 mm

but it is still smaller that the speaker itself, so we can't guaranty it would be stable /fit as intended. ):