Yes, MediaLab certainly adds to DirectRT's versatility that way. Essentially opens it up to between subject designs with very little effort in addition to adding a bunch more randomization capability (e.g., imagine DirectRT's wgr and bgr functions being nested within MediaLab's same wgr and bgr functions!). And the combo also adds the capability to throw in more traditional questionnaires before, after and between the more resource demanding precision stuff that DirectRT does.

To be fair though, I'm not sure if DirectRT can or cannot do what you are describing. It certainly can independently randomize trials within blocks and also do so with the within-block randomization being independent. BUT, this could mean many things depending on what constraints you have in mind. Feel free to post a more elaborated version of your design query in the DirectRT: How to... section of the forums, and I can probably give you a better answer!

Updayte--> strike that last comment--I see you already have: http://www.empirisoft.com/support/showthread.php?t=5333. I'll take a look at it now.