No matter you login imeem.com or not, you can download from this website both.
Firstly, Install Free Music Zilla and make it run.

Next, when you visit IMEEM™.com and play the IMEEM™ music. The playing music will be grabed by Free Music Zilla.

Select the grabbed IMEEM™ music then click ‘Download’ button. The IMEEM™ music will be downloaded.Please download it before ‘Leech Timeout’ count down to 0 and keep the music is playing when downloading.