My old Ibanez SR1206 used to have ADX6 soapbars as well. Here's a picture of the same model:
http://www.ibanezregister.com/images...r1206tk-96.jpg
If I remember correctly, they were just about the same size as the EMG "40" series, at 4.0" by 1.5". (In fact, I ended up replacing these with an EMG 40P and 40DC.) So any of these pickups should work, as well as Bartolini "M46" or SGD.
The big concern is string spacing. Make sure your replacement pickups have coils that go just about all the way to the edges of the pickup shell. Otherwise you'll notice that the outer strings are quieter.
I've never liked using this shape of pickups on a 6-string. The new MK1-6 pickups are wider, so they should track the low B and high C strings better.