I've been through a lot of earphone setups over the years and I prefer audiophile quality.
That said, all
helmet speakers suck. Period. Too much wind noise drowns out any quality they may have.
You're on the right track with the Etymotics. They offer outstanding sound, especially the highs. Shure in-ear's seem to favor the bass end, but that gets to sound rather poor on the bike with the low frequency wind noise.
I've been through both the ER-6 and the more bassy ER-6i. The main difference is the silicon flange between the two: the ER-6 has two flanges and the ER-6i has three. The seal of the ER-6i makes the bass stand out a bit more as the seal is better. However, when I wore the ER-6i under the helmet the sound canal often got pinched close and it was a struggle to get my finger between the helmet and me to work the thing into position where I could hear anything. It was less of a problem with the plain ER, but sometimes they too got twisted.
To the rescue came Sensaphonic's. They offer a sleeve to fit the Etymotic's that helps seal and direct the sound to your eardrum without getting pinched off under a helmet. Here is the link to their Etymotic ER series sleeve.
The cost was around $100 plus $25 for the local hearing aid guy to make the impressions.
Down the road I was intriqued by the molded in-ear jobs that you see at the bike shows. I had a set made by the National Alliance for Hearing Preservation at one show. They sent them off to Westone (the hearing aid company) and the set I got back from them were outstanding! Fit was very good and the seal was good as well (very important!). They are a clear hard vinyl and very easy to clean. They fit so well I can wear them all day without discomfort. They sort of corkscrew in. Keeps the wind noise down to a minimum as well. The cords exit straight down and the helmet goes on without a fuss with the phones. Cost was around $350 at the show and I had to wait a couple of weeks for them to show up.
Later, I went back to Sensaphonic's for their ProPhonic 2X in-ear monitors.
These have dual-drivers in them so the sound should be better. However, the are expensive at around $700 as I recall. The cords go up over the top of the ear on sort of a springy wire. I sent them back for a re-do as the fit wasn't as good and they had a leak around the ear and the sound quality goes down dramatically when they don't seal. The re-do wasn't any better so I gave up on them and they are buried in a drawer somewhere. They do sound good if I press them in to seal and that seems to be the trick with any custom fits.
So I'm back to the Westone's......
Regarding the AutoCom, they do make an in-line cord that has a stereo earphone mini-jack on it and you can use it with their microphone or speaker.