I have a 788/CL-8 and now considering moving to the 664/CL-6. Here is my comparisons. It's not an easy choice. ( All prices are from B&H website)
788T-$5995
CL-8-$985
total-$6980
weight
788 -3.75lbs
CL-8-21.5 oz
It's a full pound lighter than the 664/CL-6. (that's 25% lighter)
Smaller footprint (and I don't have to buy a new bag)
Full high quality metal construction
8 mic preamps vs. 6 on 664
Higher quality recording up to 96k (more dynamic range and less harmonic distortion that the 664)
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664-$4595
CL-6- $1595
total- $6190
(Only $790 less than the 788/CL-
664-4.75lbs
CL-6. 21.5 oz
664 is Larger and heavier and requires building a new bag
12 tracks (but only 6 have mic preamps, all other inputs are line only)
Separate external slate in
Panning
10 pin out and more outputs
(but 788 has more capability for output assigns)
2-returns
Color display
CF and SD card/ no HD
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Like a lot of people, I was originally attracted to the 664 because it seemed to hit the right feature/price point. But now that the price has increased and I've had more time to compare the two I'm not as excited about the 664. The price difference between the 788/CL-8 and the 664/CL-6 not that big.
I was also attracted to the ability to have 12 tracks! But having less mic preamps and less quality audio is a big trade off. Here is a quote from discussion at gearsluts:
"The 664 has nice specs for the money but doesn't compare to the 788T for critical audio applications. The 664 mic pres have 22 times (0.09% vs 0.004%) higher harmonic distortion then a 788T and the A/D converter has 12 dB less dynamic range (114 dB vs. 123 dB on the 788T). The 664 has a total of 19 bits of usable resoultion from its "24 bit" converters, while the 788T has a usable resolution of 21.5 bits of the 24. The extra cost of the 788T also buys you (2) more high quality mic pres. Of course the 664 specs are fine for many mid-range applications, and it sure looks pretty. It's clearly aimed at film/video applications."
So trading more channels for less quality audio really starts to level the field even more.
Despite all this I was hoping the 664 used less power. After talking to Sound Devices tech today I found out the the 664 uses the same amount of power and runs just as hot as the 788. Plus the AA batteries will only power the 664 for a few minutes.
So what's left? I like the color display on the 664 and the black finish. I like having pan knobs and more outputs. An SD card is convenient but I don't like having less storage.
So it's 10% cheaper but bigger, heavier, records lower quality audio, has less mic pres, less storage, gets just as hot and uses just as much power as my 788. But that color display do look cool :-)
One final note; the 788 was designed from the ground up to be the best, not a compromise. It has been battle tested, road worn and proven itself over and over in the field. It can take the worst you can throw at it and still perform like a studio console. The 644 is a great addition to the SD lineup but you can't take anything away from the 788.