Here are the installation directions:
The archive will unpack to a folder titled "RTcmix-2.00". Move this entire folder intact to the "/Users/Shared/Max 7/Library" folder. Restart Max/MSP and the new [rtcmix~] object should show as: RTcmix music language, v. 2.00 (RTcmix-maxmsp-4.2.1) in the Max console. NOTE: Be sure to remove any of your older RTcmix or RTcmix-help folders from this /Users/Shared/Max 7/Library folder.