If it isn't quick enough spooling you should look into using a quick spool valve, which diverts the gasses on one scroll to go thru the other, which means for the gas to pass thru the smaller volume it has to increase in speed which in turn spools the turbine faster, then at higher boost levels...
If you are interested in understanding how the twin-scroll system works have a look at this link: https://www.mhi.co.jp/technology/review/pdf/e501/e501023.pdf , it is very important the firing order of 1,3,5 and 2,4,6 are grouped, and the firing order of a 12-ht is 1-4-2-6-3-5, which is...