elkano are you running the ninja without the fan? If so what temps are you getting on the CPU?
I have just ordered one myself after much research and like you would idealy like to run it fanless. I have a AMD X2 3800+ CPU. I have my two case fans running on 7 volts fixed.
The other option that I thought of yesterday but not sure if it would work would be to turn the heatsink fan so that it draws cool air from the side opening that I have had blocked off till now. however my concern is that the rest of the airflow in the case would reduce so just keeping that as an idea for now.
The current heat wave is ideal for finding out how your media center handles heat

