HD-Doh!
I think that corporate's biggest problem with HD radio is that they don't know what to do with it.
If you program "companion" programming to your main channel - i.e. "Adult Album Alternative" next to "Classic Rock" - you take the chance of losing audience on your main channel.
If you use HD to counter-program the competition - i.e. "Contemporary Country" next to your "Classic Rock" station - you take the chance of reminding your audience of (much better) programming elsewhere on the dial. There's also the possibility in diary markets that any audience you get will write down "the country stations" slogan or calls and get credit even if they're listening to your programming.
Buffalo's NPR station brings up an interesting case. WBFO is very successful with many hours of Blues on the weekend. Yet, what did they offer up on HD2? "Alternative" rock, a format that's unlikely to motivate most of their listeners, who are 45+, to reach for their HD dial. On the other had, Star, a "Hot" AC that's targeted toward 25-45 females, put Blues on their HD-2. Somehow, I don't expect a lot of 45+ males, who are the core Blues audience, to discover Star's HD-2 channel.
Which brings us to what might be the correct stance. Whatever age/sex demographic target you have on your main channel, stay in the age group, but skew toward the other sex on your HD-2 channel. If you're targeting Whiny 18-34 Women on your main channel, target Emo 18-34 Men on your HD-2. If you're Classic Rock on your main channel, go Classic Singer-Songwriters (OK, all Carole King, James Taylor, and Jackson Browne) on your HD-2.
See? It's easy.
Note to corporate: "You're Welcome". Send consulting check to, uh, DAMN THIS ANONYMITY IS ANNOYING.