The amplifiers on the Prototype VI amp board are oscillating. According to the documentation, the amplifiers will oscillate if the amplifier bypass capacitors have too much inductance to ground. This is the case with the capacitors I purchase. Also, the ground and power traces to the amplifiers are way too narrow creating even more inductance. Ok.. lesson learned.

Instead of doing an entire new amplifier design and layout, I decided to splice-in some amplifiers that I could build from a kit. I decided to purchase this kit from AudioSector. This kit uses LM4780's which are a higher power version of the LM4765's on the amp board. Basically, it is the same design with better layout and higher quality parts.

Here is a picture of a fully constructed amplifier. You get two of these in a kit. These are non-inverting configurations with input DC blocking input capacitors. The gain is set to 9.15 on each amplifier. The DAC's peak output is 2.5V so the amplifiers put out a peak amplitude of 22.8V and deliver 65W per amplifier (I don't drive them this hard).
Here is a picture of the electronics. It looks like a bit of a mess (and it is!). However, it works well enough for Jon and I to experiment with tri-amping and digital room correction. Notice that I am not using the Prototype VI controller card. The controller cards are hard to build and we only have one of them. Since Jon is in Boston and i am in Seattle, we need two system, preferably identical, so we can work together. So, Jon and I are using our Phytec cards for now. The Prototype VI controller card and the Phytec card are functionally identical. Also notice the expansion card with all the red wirewrap connections. This is a major source of clock jitter that leads to distortion on the DAC output. Also, there is a audio clock (a MAX9485) buried under the expansion board that creates the mclk, bitclk and frameclk for both the MPC5200 and the DAC. Again, this goofy build-up leads to considerable noise in the system. Also notice that the amplifiers have been spliced in by connecting clip-wires from the output of the DAC filters to the input of the amplifiers. These wires sit under my fluorescent lights and pick ups several 10's of millivolts of noise. This too leads to considerable noise in the amplifier output.
Here is a picture of the entire system. There are four amplifiers in total (two per LM4780). One amplifier is connected directly to the tweeter (remember, our crossovers are in software). Another is connected to the midrange. Two are connected to the woofer in BTL fashion. The amplifiers are identical (non-inverting with 9.15 gain) but one of the signals has been inverted before it is sent to the DAC.

The process for playing music with this setup is as follows:

1. Booting Uboot. I boot the board by running picocom and then plugging in the 5V Phytec power supply. I hit a key within 5 seconds to get the UBoot prompt.
   

   picocom /dev/ttyS0 -b 115200
   

2. Boot Linux. At the Uboot prompt, I type the following command. This command has been setup on my Uboot environment to download the kernel via TFTP and then mount a file system on my development computer.
   

   run bcmd_net1
   

3. Set the Audio Clock. Before you can play any music, you have to setup the audio clock. I do this with the following command. This commands writes 0x22 to adress 0x68 on I2C bus 1.
   

   cd apps
   ./i2cset 1 0x68 0x22 0x00
   

4. Play an MP3. This has been documented before, but here it is again:
   

   madplay --output=wave:/dev/stdout some_mp3_file.mp3 | brutefir triamp.txt
   

5. Play Radio Paradise. Again, this has been documented before, but here it is again:
   

   route add default gw 192.168.1.1 eht0
   wget http://207.200.96.136:80/stream/1048 -O /dev/stdout | madplay --output=wave:/dev/stdout /dev/stdin | brutefir triamp.txt