Let me see if I have this straight. The primary job of a preamp is to take an instrument/mic level (-20 dBu) signal and increase the signal level to line level (+4dBu). The primary job of a DI is to take an unbalanced high impedence signal and put out a low impedance balanced signal. Is this correct? It seems to me that a large number of devices do both, but are labled Preamp or DI not Preamp/DI. Any real reason for this other than packaging or marketing?