Longer than 2m I'd suggest an active hdmi cable. Once you get to 5m you should start considering optical, and once you get to 7-8m I'd definitely go optical.
I'm not certain what you can get in Germany, but my standard recommendation in your price is the ELAC Debut v2, or maybe the lower end Wharfedale EVO like the 4.1. ELAC is a German company, but the Debuts are from the USA division, so again, not sure if they are available locally to you. I...