Hello Andreas! > Now, what do other K2 owners use? Use what works best for you. > And, does the K2 (and its filters, DSP, etc) support going down > as low as say 450 Hz? The K2 sidetone goes down to 400 Hz. The KDSP2 CW filter center frequencies go down to 400 Hz as well. 73, Lyle KK7P