You should have no probelm recording your 16 channels at once - as long as you've got that many inputs and the HDD subsystem can keep up ! I had no trouble doing similar at 24/44k1 on a 1GHz Celeron.
This will depend a lot on your audio hardware, I think all mfr's are working toward lower CPU load, RME has been doing this for a while, as I mentioned in earlier reply. I get about 15% CPU load on an 800 Mhz Sony Notebook, recording 6 channels at 24/96, with RME Multiface/Cardbus Interface.
Rgds,
Rick Z