I have really shit hearing (I wear hearing aids but not when I’m on the bike). I have a Schuberth C3PRO with the SRC system and have covered thousands of miles from Denmark to Italy using it. I wear the squishy ear plugs but can easily hear my sat nav and music through the helmet speakers. Even at silly speeds on the autobahn. In fact I feel that sound is better when wearing ear plugs (I have often wondered if they are set up for exactly this purpose) as without ear plugs the sound is a bit tinny but with ear plugs the sound is just right. I did have to play with the positioning of the speakers a bit at first. I used the Velcro spacers provided to get them closer to my ears but once in the right place they are brilliant. Don’t just stick them in the recess of your helmet and expect them to work best straight away. Our ears are all in slightly different places (but generally on the side of our head) so experiment until you get the best result .
Just my opinion......
Exactly my experience with the Sena 10U, much better sound quality with speakers and earplugs than my past experience of using the Ultimate Ears, and ample volume.