No, this is the right forum. I think the reason that no one has responded is that few have heard both.
In general, Headroom is pretty honest and prices pretty accurately. The difference won't be night and day, but will be the difference between good parts and cheap parts. Without decent phones you won't hear the difference, but with your Grado phones you surely will.
Headroom also has a pretty generous return policy, so you could buy both and return the one you don't like. If doing this, however, you should tell them as it is polite, and they may have a loaner or something.
I have the total bithead and would recommend it, but I haven't heard the regular bithead. The built in DAC is great for laptops (desktops to for that matter). However, it can't compete with a non-portable amp in my opinion. I would probably just pick one and not worry too much about it.
I spoke with the HeadRoom guys. They say sonically, I would not notice any difference between the two. On machine plot, total bithead looks slightly better and since it uses better components it may last longer. I ordered the regular one..