Putting speakers in a good helmet is not difficult especially if you can remove or at least get under the padding around the base of the helmet. I have the Shoei X-11 and it was a piece of cake. The speakers I used required you to apply an adhesive velcro pad where the speaker would go then all you had to do was press the speaker onto the pad, same for the microphone. Then all you had to do was route the wires under the padiing to where ever you wanted the attach point to be.
Having said that I ended up switching to Challenger custom molded ear phones. I had always used ear plugs and turned the volume up so that I could hear the speakers through them and that seemed to be working in opposite directions. Now with the ear phones, I am killing two birds with one stone. I have my hearing protection and the volume required to hear all my "stuff" (Xm Radio, Cell Phone, V1 Radar Detector and GPS) is set at a relatively minimum level. The other benefit is that as I go faster, I do not need to increase the volume on anything at all. I hear the same at virtually any speed, at least through 100 mph.
The trick with using the custom molded phones is getting them fit correctly. They send you a kit which is easy to use with another person helping. Inject the goop into your ear as directed, then as it hardens move your jaw around as well as pulling a little on your ear itself (about 30 seconds). Do this with each ear, send the molds in and in a couple of weeks you have a great set of custom molded earphones with a 3.5mm plug on the end.
I have worn them on an 8.5 hour ride only taking them out at two gas stops. Although it does feel good to get them out at a stop for awhile, just as earplugs would, they are not uncomfortable on a long stretch of riding. Add in the benefit of very clear sound, I am sold on the custom molded ear phones. B)