problem with subs cutting with bluetooth

OK.  So, if your phone supports A2DP Bluetooth protocol and is properly paired with the DDX418, it should stream music properly.  If on the other hand the phone does not support A2DP or is not on Kenwood's list of supported models, then the head unit may be cutting out the subs because it thinks the BT information is a phone call.  Assuming your phone is properly supported by Kenwood, if the subs are only turning off via the phone and they cut off every time you try it, you could have a setup parameter wrong in the HU.  I would try resetting the HU and setting it up again from scratch, and if that doesn't work it may be time for a visit to a local Kenwood installer for some hands-on assistance. Support the12volt.com

Sounds like a connection issue between your subs and radio and not the phone and radio.