When you need to test a new modualtion scheme which are not avaliable in @DS, your can use MATLAB to generate I-Q signal and then use DAT format in @DS to import the data. In another case, you may need to test , say an equalizer, in matlab. you can use @DS simulate the effect of power amplifier, filter, etc. then jusy bring it back in matlab to test an euqalize. @DS can do this as well by using Patolemy, but if you r familar with malab and simullink, it is faster and easier.