I understand the Roland R26 to be an excellent 6 track recorder, however, I don't own one. In the absence of an immediate reply from anyone using your set-up, it would help to understand your problem if you could provide a full answer to three questions:
1. What are you trying to record in terms of subject (species and number) , distance and environment.
2. What exactly is the quality problem? For example - low volume, distortion, wind noise, hums or mechanical noise?
3. Precisely how you are connecting your ME67 microphone to the recorder, which version of the K6 are you using?, are you using a suitable cable terminated with an XLR plug to connect to your recorder or are you using a cable terminated with a jack. If you are using an XLR terminated cable are you using 48v phantom power into your K6?
With this information it is possible that someone may be able to suggest typical answers to your problem even if they are not using identical equipment (and it will still help them if they are). If the hardware side checks out we may be able to consider how you have set up the recorder in a future response.
I apologise for asking you this detail but as many on this thread will agree it is about the only way that we are likely to come up with a good answer.
J