The Bt878 chipset is fairly common on TV tuner cards. The chip has a built in analog to digital converter with a sample rate of 119kHz to 448kHz, well above the standard audio rate of 44kHz. The hardware has to be hacked a little to inject your signal since the chip is usually receiving audio from the turner. With some driver hacking this chip can be pushed to 896000 samples per second. Recent developments make things even easier with ALSA support.