I use ear plugs and have no problems hearing my autocom.
Are the speakers in the right place?
+1
I use Howard Leight Max with an NR rating of 37dB.
When I had my first Autocom (Active Plus) I was unable to hear much above 70mph. I then read on here how critical speaker placement was and set about getting mine to an optimal state.
Firstly the ear wells on my Arai accommodated the Helix (flappy bit) of my ears so the centre of the speaker was too far back. I trimmed the foam under the lining slightly enabling me to move the centre of the speaker forward and over my ear canal. I then made some foam stacks with opposing Velcro on each side, this meshed with the Velcro already in the helmet and the Velcro on the backs of the speakers themselves. This raised the speakers so that they just brush the outside of my ear. They're under the lining of the removable cheek-pad (which, in my Arai also incorporates the ear recess). This is all day comfortable and made the Active Plus much more audible at higher speeds.
At the time I was using a Garmin StreetPilot 2720 and a small MP3 player. The SP2720 has speed sensitive volume which helped.
Since then I upgraded to a Super Pro Avi which increases volume automatically dependant on background noise. I'm now running a Zumo660 (which lacks the speed/volume thing that the SP 2720 had), a PMR radio and a Bluetooth dongle that connects my phone. Yes, wind noise is intrusive but I can still hear sat nav and bike to bike at Autobahn speeds (100mph+).
If you haven't tried adjusting the positioning of your helmet speakers give that a go first as it does make a difference at higher speeds.
Granted in ear monitors might improve audibility further.