What was wrong with the D2C Pro? With many older modchips it is possible to run most, if not all, of the newer games with patched discs and/or Trucha patched IOS. So, it may not have been necessary to remove it. The reason why I asked about using the D2CKey firmware is because the D2C Pro appears to be a clone of the D2CKey; however, I don't know if it can actually be programmed with D2CKey firmware. In another thread, Wiisel reported that D2CKey has a working GC audio fix. I have not verified that myself. Did audio streaming games work properly with D2C Pro? If D2CKey works with a wired install, it should work with a Wii-clip (though my experience has been that Wii-clips are not too reliable). I do know that Wiikey 2 messes up audio streaming, as do Wiizard and Wasabi Zero.
YAOSM 3.2 works perfectly, and might be worth looking into along with this
D2A drive controller board. But I would still suggest going the USB route with a softmod instead and wait for DIOS MIOS to add audio streaming support.