Ricardo, I found a 'manual' way, which is exporting .csv file to digistore product database.
It's a success, but 1 problem, though. Joomla! can't recognize the picture file from the data feed. I have to do it manually through DigiStore's product manager menu... and doing this for 100+ products is no fun at all

Are there any ways to automate this? (or a hack so that Joomla! recognize my picture file paths?)
Thanks