I read the article about badbios and would like to present a possible solution to these problems.

To address the speaker/microphone avenue of communication, I recommend the raspberry pi model A. A model A has 256mb of ram, which happens to be the same as the minimum requirements to run armory offline. In addition, since the model A doesn't have wifi or an ethernet port, you won't do are less likely to do anything stupid, like connect it to the internet.

Now that you have a computer that is next to impossible to connect to the internet, you need a way of communicating with the outside world to sign transactions.

I'm not sure if this is possible at the present time, but it seems to me that the best way to do this would be through qr codes of some sort--I'm not smart enough to make this work, so that is a slightly fuzzy part of this suggestion.

If you want to go the uber-paranoid rout, you could use an external battery pack to power the pi, which completely isolates the pi from any possible source of malware.

I think that this system would be as secure as it gets, but if I anything I said is wrong, I'm sure you'll let me know.