Background:  I've been using the 20S for a few months happily with a 2013 Ultra.  Put about 10,000 miles on it with CB, XM, intercom, etc.  I wear NRR 33 earplugs every time I ride beyond the parking lot.  It has not only not been a problem, the 20S with a 3/4 helmet and that bike was my daily driver and I loved the setup.

I now have a 2014 CVO Limited.  I do believe the year is important as it's when they started in with all the integrated stuff, nav, etc.  I no longer need the 20S as my phone connects to the bike and I can use the headset and infotainment system with my phone.

Not a problem, I've had to put the cap on the Harley mount kit and use it without the 20S and it did just fine. 

No more.  It really, completely, and utterly sucks with this bike.  At a stop light and until about 25MPH it's fine.  25-40MPH and you can tell the words to a song and you can talk on the phone or CB without too much trouble.  At highway speeds, 60-80, you cannot tell if a song is on or if it's the DJ talking.  You cannot hear the CB at all and you might as well leave your phone at home.

I am so glad I tried that out before I went on a 400+ mile ride with a whole bunch of other people in my chapter.  We use the CB constantly and considering my wife has had heart surgery I really like keeping able to receive phone calls should they be necessary.

I switched back to the Harley headset and I could hear fine at all speeds.  I could use the phone, CB, listen to XM the whole way.  

When I got back into town I tried out a few things:

20S  with cap on Harley mount (no 20S) no-go.  Unusable after about 45MPH

20S mount with NRR 20 ear plugs - eh.  I don't like the ringing in my ears.  I flew helicopters for too long to screw with my hearing that much.

Earphones plugged into 20S mount - MUCH better but I really don't like the idea of yet another thing to plug in.  I might consider this for longer trips but I really don't think it's worth it.  I'll just keep the Harley headset as it works with earplugs and no earbuds required.