It's not possible to transfer the tunes from/using RCA EasyRIP to the iPhone 6 device, because this is an application that is being used to manage the contents of the M4508 8GB digital media player. The software wasn't developed for this procedure, however, there is a way, the classical way. Simply transfer the music from the device to your computer and then use the classical way to transfer files. Download and install iTunes (the official application used to sync music) and connect the iPhone 6 to your PC. This is the recommended and easiest way.
Download iTunes: http://www.apple.com/itunes/download/