Another TTS Navigation Question

I'm so sorry to be asking this question because it's entirely likely that this question is answered somewhere. But I've read a few, and some people's questions are marginally different and admittedly I'm a bit unsure I understand the answers.

I have a Samsung Galaxy S4 and with version 4.4.2 on it. I've recently purchased a Toyota RAV4 LE (although admittedly I had this same problem with my last Corolla), and it has the base model Entune radio that features Bluetooth. Prior to installing Soundabout I had problems where if I used the Google Navigation, the instructions wouldn't be audible over the radio if Bluetooth was enabled. Instead there is a Bluetooth output and that's where I'd hear it. Problem is that I don't have music on my phone so I wouldn't hear anything if I left it on that station to hear the navigation.

A friend suggested Soundabout, and I've set the TTS to be Bluetooth Mono. This enables me to have my radio on, and the output from the navigation actually plays over the phone's speakers. Admittedly I'm really new to this app and trying to solve my own problem. What are the different settings? Is there any way that I can get the navigation to play over the car's speakers with the radio on? It's so bizarre because if I get a text message it will read the text message out loud over my speakers and actually interrupt my car radio's output to do so. That's what gave me hope that maybe I can get the navigation to play over the regular speakers while I'm in Radio or even USB mode. Thank you so much in advance for any advice you can offer. I hope I don't sound too clueless!