I love my Sena SMH10. It is the only one that sells an accessory mounting plate that allows you to plug in your headphones or earbuds of choice.
You want this:
http://www.senabluetooth.com/products/acc_SMH-A0303.phpSena's Electronics modules are the same. This mounting clamp has a boom mic (which works in either a Full-face or 3/4 helmet) and a 3.5mm jack for your phones.
You can put in whatever phones you like the sound of that will fit. I am using Koss KSC75 Portable Stereophone Headphones ($16 at Amazon). These puppies fit my Shoei and have amazing bass response. Take the earclips off, they just snap off. They're loud too. Heck, open your wallet and get some Sennheisers.
The trick is to mount them in your helmet with a small piece of foam cushioning, about 3/4" thick. Use Silicone glue to mount the foam to the helmet shell, and more glue to mount the phone to the foam. The foam acts as a spring. It retracts a bit when you put the helmet on, and the expands back so the phones just contact your outer ear. If headphones don't touch your ear, you will loose bass response rapidly. Not so tight that it's painful, just enough to touch. Takes some fiddling and cutting the foam to the right thickness for your ears. Much better than the crap headphones they sell, which are all-midrange intercom style phones. Leave the stock foam covers on the phones for cushioning comfort, or get some that are bigger for your particular ear.
The only downside to the Sena is the bike-to-bike intercom distance is very short. But I don't want to talk to anybody anyway. I use old fashioned hand signals.