I personally would not try it, but it works for some, and it doesn't for others. You never know until you try. If you can afford to take a loss, god forbid that happens, then I say go for it!
I;ve only seen it done several times.. and both times it was a tank with 5 silver and 2 jardini...
But i've never own that much arowana at one time.. so never tried it myself.. also my silver and jardini are wayyyyy far off from being housed together...
On the contrary, this might not be a good idea, as silvers grow A LOT faster than Jardinis, and before you know it, the silver will have that jardini in his mouth
You could solve this problem by buying mid-full size adults, but then there is the aggressive issue that resurfaces.