Different applications need different solutions.
Yes it is off topic but I was talking about PA-tops and wedge monitors. Considering the reinforcement of voices and vocals which is a different animal (yes it is off topic), that means that some forward edge around 1..2kHz is sometimes a benefit, of course it is all depending on the acoustic situation of a given room.
Back to topic.
The Orange AD200 provides a very significant edge around 1..2kHz (and above). This Orange typical boost is a firm component of the Orange Schematic design. It cant't be switched off and is therefore present all the time, no matter which EQ settings are used.
Hiwatt design works similar but the Hiwatt static Boost is rather focused at the treble band.
Orange schematic was designed at a time period where most of speakers provided muddy sounds, mid scoped with reduced treble range.
So the Orange design has it's most permit on vintage speakers of the 70s or similar vintage designed stuff.
Hiwatt's treble Boost is more smooth and therefore works perfect even with modern designed speakers like 15PR400/3015.
My suggestion for the AD200.
Neither 15PR400 nor 3512.
At least the 15PR400 because it has not any peak where the AD200 is very strong anyhow.
But I would keep on looking for something like 70s Vintage sounding.
Don't get me wrong but it is very hard to give any advice for any (vintage) amp that is coloring at the high mid band very strong.