Wow your tank look like a battleground. I would put in the jag since you already have that many aggressive fish... Why not try. Oh you should get some dither fish like silver dollars or convicts.
the silver arrowana unlike the jardini is pretty harmless as already said..it cant do anything to the other cichlids u mentioned if they r of a similar size..but considering the sa cichlids u hav kept..it is very likely that they vil soon fight..look out for the fh..it is quite capable of severely injuring the others..i do not recommend adding a jag as it vil only increase the fighting..by the way the jewel cichlids are soon goona get killed.
How did you make it this far? I agree with the person that said you need dither fish, that might give your cichlids something to focus on instead of eachother!!!
Doubt adding the jag to the tank will make much difference as the combo of cichlids is already quite shaky. Keeping a community such as this is ever changing and what may be working for weeks can quickly turn into a disaster. As for the silver arowana, the tank will be to small once the aro reaches 24".
Not sure I understand your question, looks as if you are already keeping the cichlids with the aro. The issue is the tank will eventually be too small for your arowana so the arowana will need to be moved,