Which DAC would fit me best?

I would appreciate any help that I can get, as I've been reading reviews of DACs for the past week and have no idea what to get.
-My budget is $400, I'd like to spend less, but let me know
-My headphones are BD DT880 '03
-My amp is a Little Dot MKIII
-I'm using my MacBookPro as my source
As far as music choices go, I like to listen to some modern Rock, Jazz, Classical; so a pretty fair range.

I know it all boils down to just jumping an picking one, but I'd love to see if anyone had any specific recommendations based upon my setup.
I'm using the DAC in a Behringer DEQ2496 (I also use it for room correction), and the same DAC is available in the SRC2496 (whcih I am also using) for $200 new in the US. It does require use of balanced XLR to unbalanced RCA adapters since it is a pro audio unit. There are certainly better DACS out there but I like the sound for the price.

Thanks for mentioning the Little Dot MkIII headphone amp, I was unaware of these, looks really interesting for $200. I have a pair of Grado SR325 phones, the headphone output on the SRC2496 is OK, but it uses a lower quality DAC than the main analog output so it would be nice to have a better sounding headphone amp like the Little Dot.
The DAC1 from Benchmark has a good headphone amp. I'd get that if I were looking for a cheap DAC to use with high quality headphones. I doubt you will find it used for much less than $800 though.
Used Benchamrk Dac 1 w/o usb - cheapest I have see here though was $675. Definately worth it if you can swing it.
A 40 regular, maybe?
I've heard really good things about the $400 Cambrige Audio DacMagic - balanced outboard DAC. I've not heard it myself, but I know two people who told me that it is a fantastic bargain. It has been getting good press too. If I was in the market for a $400 DAC, I would definitely want to audition this one.
At $400 I would look for a used Paradisea here on AGon. My Musiland MD10 (USB)($300 new)is great, but the Paradisea is better.

Just guessing, but I think the Paradisea would also beat the Dac Magic.
Though I haven't heard one specifically, I'd second the Paradisea as it's MHDT and close to the Havana. I'm happy with the Havana after owning a Musiland MD10, a Benchmark DAC1 and Bel Canto DAC3. More laid back, albeit not near the jitter control of the DAC1 or DAC3.
I personally think the Benchmark DAC sounds terrible - thin, amusical, artificial.

The MHDT DACs are all outstanding for the money. They are all in the NOS/filterless which to me is the best way to do digital.

I use a MHDT Dialogue at the office. $200.
The DACMagic lifted my modest system beautifully, even right out of the box. Yes it's a fantastic bargain with features I can grow into. I've long been curious whether the 24/192 DAC in my player can be improved with an outboard processor and I'm happy to discover it did. Give it a try.
mhdt paradisea and replace the stock GE tube with a NOS Tung Sol equivalent for a more full range sound with better authority in the low end.
I have been happy with the Apogee Mini-dac. It could replace your amp as it includes one. You can find them for $600-800 or so.