This looks wery like the original Futura solution of Zodiac. but what you are describing about handling is in slow speeds yes?
I guess that your problem lies in the fact that you have added bouyancy to your boat and thereby disrupted your steering stability in slow speeds. the added tubes will in fact not give you less handlingstability at higher speeds because of now you have in fact two keels and the boat now is an catamaran.
The main issue is rigth pressure in all the tubes on your boat and that is usually a lot higher than you imagine.
I myself was amazaed when I started measuring this.
the result is a mutch more rigid body and the boat less influeced by the surroundings.
I own a Zodiac Futura MKIII 470S, engine of 55Hp the top speed is approx 45 knots (ticked on GPS).
On this rig I used a ProPulse adjustable composite proeller this gave me the speed of 45 knots in ahead fair breeze.
But since the boat weigths just 90kg and the engine likewise, the rig is wery tikly in windy conditions in highspeeds.
A SIB is allways more influented by the enviroments like wind and so, due to the fact that it has a smaller portion of the body in the water and there by a huger body in the wind.
It's like a ball on the water. you can newer sink it but you can capzize it.
(bare with my bad English, I am Norwegian by birth).