Help needed- getting digital rights back from a traditional publisher

Hi everyone, wanted some advice, especially from those of you who have been published with a `traditional' publisher. I published a non-fiction book on Marketing in 2007 with a major NY publisher- and it did well enough- got a half decent advance, and it's sold >3000 copies, which given its niche is not too bad, and got some big ticket endorsements. I started my Kindle experiment in March- when I put up 2 novels for which I had digital rights from my backlist- and in the next couple of months will be putting up my first `straight to Kindle' novel. So far, my experience on Amazon has been heartening- nothing that may be worth shouting from the rooftops about- since I know many of you have sold many more ebooks- but I'll end May having sold just over 600 books on Amazon. That got me thinking about the non-fiction title and I wrote to my publisher about getting back digital rights- since they haven't put an ebook version up- and asking them if they have any plans to do so. I haven't heard back much and feel like I'm not getting a very clear answer- either they plan to put up in ebook format or not- and either they're ok to have digital rights revert or not- but I'm getting bounced from one person to another on email.

I had a very good experience working with them- so I definitelty don't want to burn any bridges- and they editor was a great person- so what do I do? Maybe they're slow on the digital wave so they don't have a process on how to deal with such a request or maybe being a major global firm, they need a lot of approvals- whatever the reason, I'm not getting much by way of a clear response.

Any advice on what I could do?

cheers