These amps where designed by a friggin insane person.
Throw it back in the bin, Now!
Seriously, there are 4 sheet metal tangs that hold in the 'box'.
Remove the 4 nuts, push in the screws (they are glued tight & they come loose when you reassemble it), lift out the box.
The speaker connections must be removed from the zobel board.
The IEC connector ground wire must be removed.
And finally, there is a 16 pin header that connects the power amp to the front panel.
That must be removed.
Reassembly will earn you a 16 pin connector that is a PITA to get back on, cuts from the sheet metal & an unreliable POS of a powered mixer.
I do not post this out of vengeance or malice but as a caution.
(I just repaired one & I swore, "not again")