I should say right off the bat that I don't own the 910HD, so take what I say with a certain grain of salt...
Having said that, I can tell you that the common review of the 910 is that it will cut your FM range significantly even if you wire the car's antenna directly to it without splitting it.
The reviews are mixed, but my read on it is that unless you are driving inside of a major city, the 910 won't work well for you. I'm not sure if the problem is with the pioneer engineering or with HD radio itself, but the common conclusion I've found is that unless you really want HD radio a