just bought Bose Companion 5 speakers and they produce very nice sound for what I need it (home use). The speakers should be connected to PC via USB cable for full performance, however there is also a Control Pad that has AUX jack as an input. When I use Traktor and output sound to Bose Companion 5 with RCA to AUX cable and set audio setup in Traktor DJ as Traktor S2 , everything works fine except the fact that there is some single tone frequency noise heard in the speakers once I plug the AUX cable in the Bose's Control Pad input. However, if I change the audio setup to Bose sound system and plug the RCA to AUX cable into MacBook Pro, the sound is more powerful and clear (and no noise of course). The problem is, that I cannot use the headphones with this set up or I don't know how to set it up to use the headphones for song syncing. Is this even possible ? If not, can I at least get rid of the noise with the first set up if I buy a better quality RCA to AUX cable ?
I have 14 days to make up my mind if I'm gonna keep Bose Companion 5 or return it, so any help will be appreciated !

Thanks in advance!