What if my source doesn't support aptX®? Can I still use B1 and if so, how will it sound?

You can absolutely still use the B1, and it will sound great. aptX® is a high quality Bluetooth audio codec that works really well. With that said, in addition to mandatory support for SBC, Bluetooth also includes optional support for many other codecs, like MPEG-1, MPEG-2, MPEG-4, and AAC, all of which have their own advantages, and some of which sound very close to aptX®.