GDM,
The N501-8B may already have the 30923 ( padding with some HF contour ) built into it.
That's the speculation ( anyway ) according to this
older thread on the subject.
The info is not corroborated of course ( that's nothing new regarding older Altec stuff ), but there are some strong inferences .
The Jabo ( type ) horns additionally focus the HF into quite a laser beam >> therefore the need for ultra HF compensation is really quite mitigated vs say a typical Altec sectoral/radial .
That's why I replied earlier, it'll likely "be fine" ( conditional on individual taste , obviously ).
Ps; There's just no substitute for making personal measurements and then using them to identify one's own preferences.