Dynaudio just got back to me saying my DBM50s were faulty after all. They should go down to 46Hz +/- 3 dB. The person I talked to before turned out not to be from Dynaudio, but from TC Electronics, their distributor.

So now I'm reconsidering the DBM-50s. Is there anyone who has worked with them and can confirm or counter what I heard (nothing below 65Hz)?