makem said:I'm sure the OP knows about those things. He asks if the levelling board is strong enough.
I have put all my 86Kg weight on that board whilst it was in place and it survived. It really depends on the area over which the 26k is spread. 26k is just the weight of a suitcase taken for a holiday so a large amp should be no problem. If it is small and tall then spread the weight with a small piece of 5 ply wood.
If the board is removed to take the amp then you would have to lean over with the full weight to put it in the boot. Not good for your back.