Hi!
Maybe somebody here was same issue like me: So i have N1996A, 3GHz version, with A.02.04 GUI version, in my lab, and i activated options 506, P06 (and edited profile for 6 GHz like in post above), 1FP, AFM.
Everything works great, but after that i decide to activate SR6. System says ok for option key, and key is appear in option list. But button 'Stimulus/Response' in 'Mode' menu is still disable!!!
Maybe it need to edit some profile for 6GHz SR6 like it was with P06?