I understand earbuds on a motorcycle are illegal in many states. Even when they are legal they don't offer the ambient sounds to get thru (sirens, horns, etc.) as well as a good set of helmet speakers. I have the Sena SMH10 also. About 6 years worth. Even replaced Sena battery about 2 years ago. Went thru the same problem with sound volume and quality as you are experiencing. But, after I replaced the stock speakers with IASUS speakers (from Amazon) I no longer miss my ear buds.
Just my 2 cents.