XPS 15 9570 Can't hear Line In Audio

Greetings, DELL Community:

I've got a CASIO SA-76 keyboard running into my new DELL XPS 15 9570 (Win10) laptop for the purpose of recording some music in SONY Vegas PRO 11.  I selected "Line In" in the MaxxAudio Pro Pop Up window. Though I see an indication that the sound is registering in the computer, I'm not hearing it through my ActivBuds S520 Bluetooth headphones. Also, in the MaxxAudioPro window, the "Recording Device is not available" message keeps showing. How do I fix this? Do I need to update a driver or uninstall something???I need to fix this soon as I'm creating music for a video project that I need to edit soon. All updates have been installed. Looking forward to hearing back. Thank you so much.