I really currently have a hard time getting a good HPEQ for my Stax SR-009. I really do not know what I am doing wrong.
Do you follow the manual? Always reset a preset and verify channel mapping and angles etc. Activate PRIR diagnostics as described in that chapter, what values do you see?
Honestly if you follow the manual to the letter and verify settings, it's not possible to a miss a channel etc. But there's many details which might be forgotten.. also check what settings you have with RECALCULATE EQ / INVERSION SETUP - maybe they are non-default resulting in bright sound etc.