I have heard many such systems and they can be quite fine but they are rarely made from consumer stuff. Even so, the best studios I have heard (in) used stand-alone monitors in controlled environments. I am thinking of Bob Ludwig's big room in Portland and some of the rooms at Sound Mirror near Boston. Besides, once the budget and space accomodations get into this realm, there are few limits other than the intelligence and art of the designer.
For the vast majority of people who even ask this question, though, my answer is more relevant, I believe.
Kal
