I woould caution against keeping bichirs (especially smaller ones) with a large oscar. This is not a very likely scenario, although not a completely impossible one -- if an oscar tries to snack on a small polypterus, those razor sharp dorsals can do some serious damage to fishes innards.
I had an oscar once a while ago that cherished nothing more than earthworms. I tried to introduce a peacock eel that was immedeately scooped up by O probably because it looked so much like a nigh crawler. Fortunately, that turned out to be just an expensive feeder. Bichirs on the other hand can take care of themselves... I guess what I am trying to say here is that you need to make sure your bichir is of compatible size before plopping him in the tank
If it was me with your dilema, I would go with a school of 3-4 silver dollars and a pl*co (to create a SA biotope ), If you are bent on having only cichlids in there, a few firemouths would make for a nice display. Or how about some honduran red points?!
