Sound card I/O and CPU usage related ?

Anyone have the answer for this.. if you have a sound card that has a lot of I/O channels does it use more CPU then one with only a 2 or 4 ? Also, does it matter if they are all enabled in Sonar or not ?

Also, does it cause Sonar to use more CPU or is it just the driver that might use more ?

It's not a clear cut thing.

ASIO drivers, and certain "multichannel" WDM ones run all channels in a single interleaved stream, so there's a certain consistency whether using 2 or many more channels, although the system has less work preparing buffers if there's fewer channels actually in use. Many WDM drivers provide seperate channel pairs, so when not tracking with multiple channels, you could concievably cut down a little system overhead by deselecting all but a main stereo pair.

The multichannel drivers should be a more efficient option if the project is using most of the available channels, however a single pair of a seperated WDM drivers channels would be less overhead IF that's all that required and none of the other channels are selected.

M-audio Delta series WDM drivers provide both multi and seperate channels (but the ASIO is always Multi).

Above all that, interfaces tend to always use the same number of bus cycles whatever the demand, usually in bursts of 32 clocks, enough for all the channels in most devices.