Most of the Dolby Headphone DSP chips entered mass production mid-summer this year, but they're not going into much consumer audio gear -- mostly just home theater stuff, especially DVD players.
Do any of you have any idea about what it would take to construct a stand-alone Dolby Headphone signal processing unit? My understanding is that all of the current chips have to be used in conjunction with expensive integrated software, but I really don't know much about it. Any of you know if the possibility of a hardware-only solution exists?
Don't bother. There was a lot of discussion on similar topics before, and basically unless you can figure out a way to get a DSP chip, don't even try. You cannot get any such chip without signing a licensing agreement with Dolby or whoever, and paying tons of money. One way you can go around that is to buy the cheapest commercial product with that chip and rip it out and install in your own board. However, the license is really for the software. You might even get a chip but without algorithms it's worthless. It's possible you can play dumb and try to buy an eval board or something from a distributor and see if they'll sell it without question. But unless you're an engineer with DSP programming experience you should probably buy commercial or at most modify a commercial product.
Also, Dolby Headphone will work perfectly in software and you can get great sound by connecting optical or coax digital out to a standalone 2 channel DAC and plug headphones into that. That's what I did with my portable DAC (any will do) and SB Audigy instead of using just Audigy Platinum's headphone out which is underpowered and not as good.