Everyone knows the advantages of using an external soundcard. The most obvious is the external soundcards have enough space on their chassis for higher quality 1/4" TRS or XLR connectors. This is especially important for recording studios that need to hook up a lot of different microphones or instruments. It's also nice for home theater setups where you have up to 8 channels of high quality audio output. It's kind of a shame to send the signals out tiny little 1/8" connectors, especially when each connector is paired so there are 2 channels per 1/8" connectors. There is also the argument that an external soundcard is going to sound better because none of the PC's components are going to add noise to the analog signal. Oh, and for very small form factor PCs, an external soundcard doesn't take up any valuable internal PCI/PCIe slots.
I just ran across an article in Ars Technica which speculates that we might see external video card solutions in the future. A new PCI Express standard has been approved by the PCI Special Interest Group (PCI-SIG) called the PCI Express External Cabling specification, which will support the development of external video cards. Since the latest and greatest video cards from NVIDIA and ATI/AMD generate a lot of heat, take up to 2 PCIe slots for dual SLI or Crossfire, and need a lot of power, maybe putting them in their own chassis outside the PC might be a good idea. Again, this would obviously work great for small form factor PCs.
What about a combination high performance audio/video box? If we added the necessary space and components to our product, we could have a pretty interesting new A/V product. Something to think about... However, since these video cards generate so much heat, they will need either big heat sinks or noisy fans. That defeats one of the advantages our product has in the market. Which is - our high efficiency amp modules don't generate too much heat, so we don't need massive heat sinks, like similarly powered Class A or A/B amps.