Foam plugs with a Sena 5s and their upgraded speakers work fine for music. I don't use it for calls or comms.
As a bass player, helmet speakers are pretty unimpressive to begin with. When moving they're even less so. Even without ear plugs. So for me the quality of music is already compromised. I can hear things ok enough with earplugs that I can enjoy it while riding. I find it helps to keep me focused. Something about keeping a part of my brain occupied so I don't distracted.
I've got custom in-ear monitors for performing. I wish they were comfortable when worn inside the helmet. That would be the way to go...