As you are well aware, the SS DSM mics are going to have no problem picking up bass whatsoever -if anything, they usually need some kind of low-cut. Similarly, the R-09HR certainly is capable of recording the full frequency range.
Do you happen to have the low-cut, limiter or other settings on the R-09HR set to "ON"? That seems to be the most likely culprit--check those switches on the back. The low-cut filter on these consumer decks is not, as I understand it, very accurate at all.
Assuming you are recording amplified music, I would, in any event, use or acquire a battery box to power the DSM-6 and run through line-in, or if you can't get a strong enough signal, MIC in with MIC POWER set to "OFF".