imo, CD3000 is probably one of the best all-around performing headphone for under $500 as well. There are other ATH headphones within that range, but they all have characteristics and strength that doesn't give them an "overall" superiority (i.e., might have better performance for certain instrument, certain genre, but not overall, always better than CD3000, where CD3000 is consistently better in most areas). ATH headphones do look much nicer though
I actually do like the way that CD3000 looks, even though it's a bit bulky, and it's a dull grey... it's still a very aesthetically pleasing headphone design overall for me.
As far as source and amp, all high-end headphones like the CD3000, HD650 (list goes on and on) need adequate source & amp for them to show their true color and why we give them their praises. Without proper setup, it's hard to judge any high-end headphone's merits. Given that, CD3000 is easily driven out of any source, reaching proper volume levels, however it is also revealing and will show thin-ness and inadequacies in your source. Just because you can get them to be loud enough doesn't mean all the sound characteristics are what they're meant to be.
I personally don't like Headroom amps that much, in my experiences, Headroom amps pairs up with Sennheiser headphones pretty well on a consistent basis; other than that, I don't see any merits in them. It is also my personal experience that other DIY amps and small amp builders build amps that's equal and surpasses Headroom's quality for lesser cost.
Is the Total Airhead (or Airhead) enough to drive the CD3000? Not even close, in fact, I don't think you'll notice much of a difference just plugging the CD3000 straight into the source. I think one of the budget option is the aforementioned Gilmore Lite, but Gilmore line of amps are also very revealing of your source, so if you've got a bad source, Gilmore will not be the way to go. Gilmore also sounds a little harsh and sterile with the CD3000, I like a little bit of coloration to my sound, so meanwhile that combination is good, it's not something I liked much personally.
One of the oft-mentioned amp to go alongside the CD3000 is the Perreaux. I never tried one of those, so I can't tell you much about it. A lot of people really loves how smooth and warm it sounds though... seems to be the general concensus about the Perreaux. It's not the most detailed headphone amp, but it makes good music.
With the CD3000, I seriously think that your "budget amp" starts at around $300 and up. Anything lesser than a $300 amp is just not a worthy investment.
If you don't have the budget to buy some amps to back up the CD3000 right now, or at least consider doing that eventually, I would seriously consider just getting an Audio Technica A900 and be done with it. If you do get a CD3000, get it with the foresight of eventually getting a good source and amp to back it up.
