[ayz]

WHat is the difference exactly, and is it worth the $150 price tag difference? 
 
I'm wondering the same thing about the FUN as well - Version A is almost twice the price of the basic version.
 
How much of this is a significant improvement in quality and how much of it is just a minor change in parts to make you shell out more cash for a (marginally) higher-end model?

 

[1stimer]

The dsp and the df are the digital filters that are used in each DAC.  The DF-1704 digital filter has been around for a while, while the DSP-1 is Kingwas own  design, which he includes on his higher priced DAC's and some who have heard both suggest that it IS worth the added cost.
 
I just received my DAC-19DF which I chose solely for financial reasons.  I cannot comment on the sound quality differences personally.

 

[slim.a]

The DAC-19 DSP uses the DSP-1 filter.
The DAC-19 DF uses the DF1704 filter.

I have had the opportunity to listen to both filters: the DF1704 in the dac19mk3 and the DSP-1 in the DAC-19 DSP.
 
To me the the DSP-1 filter is a much superior filter than the DF1704 for 3 reasons:
1. The DSP-1 is less sensitive to the jitter (quality of the transport).
2. The DSP-1 uses better filternig algorithms than the DF1704: Even at 16/44, the DSP-1 sounds very natural
3. The DSP-1 can be customized by the end user: You can choose diiferent oversampling settings (even NOS), different passband filtering, ...

In my personal experience, it is well worth the extra $150. For a more detailed comparison, you can read my review here: http://www.head-fi.org/forum/thread/483899/review-of-the-audio-gd-dac19dsp-c2-amp-the-acss-connection

 

[quicksound]

I haven't done a comparison between the two, but the DAC-19 DF sounds incredibly good paired with the DNA Sonett and DT880 600 ohms.
 
When my girlfriend first listened to music with the DAC-19 DF instead of using the iPod's sound card, she cried because it sounded so good. I must say, I was surpised at her reaction. I thought she would say "why did you spend $500 on this piece of junk?"

 

[haloxt]

Probably only several people on head-fi have heard the dac19DF. Very nice compromise between musicality and fidelity. What I really loved about it was that it wasn't detailed enough that it would force all the recording flaws and poor playing on you, but it was detailed enough for you to have a good idea of the original meaning of a song. After trying different tier audio-gd gear, I think their single-ended gear or mid-tier balanced are probably the sweet spot for most audiophiles.