Develop ear = ability to tell differnce between notes, chords, ability to not confuse volume for pitch, etc.
Cool, cool, happy hunting for the sub then. Looked around on amazon.de and it is a tough market. Might just have to make do with the Yamaha. What is the best price you are seeing for that on? Any chance you can make your own?
The location you marked with green will work fine for the sub.