It most probably has nothing to do with your current problem, but since I have the same operating system (MacOSX 10.6.8) than you have, let me just tell you that sometimes there are issues to interact with the Linux based DR, not when copying books, but rather when unzipping and installing some applications from the developers in this forum. At some stage dima_tr suggested to use iterm and midnight commander, and I have not had any problems with installing apps ever since.
Here is the relevant discussion:
https://www.mobileread.com/forums/sho...t=iterm&page=6
post # 76 (see also #63 and post #94)