NI sells a board called the NI-4552, which has 4 analog input channels, 16-bit resolution, 204.8 kS/s sampling rate. The 4552 has an embedded 32-bit DSP processor capable of performing onboard FFTs in real-time. Use the RTSI bus to synchronize two of them and acquire from 8 channels.
http://sine.ni.com/apps/we/nioc.vp?cid=1488〈=US