You can certainly use MediaLab to enhance the randomization capabilities of DirectRT (e.g., helping especially with the creation of between subject designs). However, if I understand your design correctly, you could do this probably within DirectRT if you could get your four trial components consolidated into single lines (i.e., as opposed to 4 lines within your input file). Or maybe I'm not understanding. This is the line that is throwing me:
I am using RBG to distinguish between sets of 4 trials which consist of cue, ITI, target, ISI.)
Could you elaborate or possibly attach a simple sample input file that illustrates the problem?