So, that is a complicated question. If you have loud pipes and a loud helmet, then you will destroy your hearing long before things get loud "enough." There are very few good helmet speakers, even the new stuff from people like JBL. SENA products are not the loudest on the block either. I have SENA 10, 20, & 30K models and the Packtalk Bold is both the loudest and highest audio quality. Not saying SENA is bad, just not the loudest.
If you want to hear the best music safely, you have to go with earbuds or in ear monitors. I hear guys say that they can't hear anything like emergency vehicles with earbuds, then they crank their speakers up so they can't hear anything anyway. EMI's offer the highest quality and noise reduction to save your hearing. There is a technical reason why you can hear a siren with isolating earbuds. I wear EMI's that pretty much kill all the noise, I still hear them.
Now on that BT speaker you have been wearing, If something is not designed to be in your helmet, it shouldn't be. Safety first!