FM extra would be a lot better way to go.
Howso? The way I see it, it still has several problems inherent with HD radio. There's still a delay between analog and digital because of processing times, as far as I know. And that is one of the biggest gripes with HD — bad sync.
With FMeXtra, there are no sync issues because it isn't designed to fault to the analog. It also doesn't require that any digital channel be a duplicate of the analog. It is a completely independant system operating on a subcarrier channel. Different animal altogether.
There's the issue of poor digital sound quality at low bit rates, and I don't see FMX fixing that if stations for for two or three subchannels.
Actually, FMX does a pretty good job with audio. It does depend on what you do with it. You can run two full fidelity stereo channels or break it down to as many as nine low bandwidth channels. It's up to the broadcaster what they want to do with it.
There's the issue of coverage. I don't have much experience with SCA reception so I cannot say if FMX would mimic SCA coverage areas, be better, or worse. Input on that would be very much welcome. If like HD it doesn't work outside the 60 dBu contour, that is still another problem. I'm sure the digital dropout problem would still exist with FMX because it'd drop out whenever the analog signal did since it's being packaged inside the analog spectrum.
Actual on air tests have shown that FMX remains robust out to the 54 dBu contour.
Finally, portable reception and battery life. Are there any portable FMX prototype radios out? If so, their battery life probably isn't all that hot, like HD radios. So that's one more problem FMX would have along with HD.
To my knowledge, there aren't any portable FMX receivers out there, but I believe it has been shown that they can be built and operated at a low power consumption.
The advantages I see are cheaper equipment and licensing. That only benefits the station owner.
Actually there are numerous advantages. FMX is addressable meaning an operator could sell subscriptions, it doesn't cause interference to other stations, is very simple to operate and reliable as you could ask, and actually works well. Now one of the problems is SCA isn't allowed for general broadcast by the FCC. That's why SCA has always been a subscription service of sorts (with some exceptions such as reading service for the blind), but that rule could be changed and FMX on SCA be adopted. This would open the door for just about any FM broadcaster to be a participant.
One big problem remains though. What compelling programming would you put on all of these new channels?