Documented API's ??

Believe it or not, there are people working with digital computer audio for other than music and entertainment, and for real time processing rather than recording and offline editing !

My interest is in joint, real-time processing of audio from several sources to provide real time outputs of
processed audio. 100mS to 250mS delay max!

I desire to take in audio in separate, parallel streams from multiple soucres, buffer the audio as efficiently as possible to reduce latency, process the audio in real time buffer-at-a-time to create one or more output streams, which are buffered in real time too.

Right now I can do it with 2 channels using the LINE IN and LINE OUT audio jacks on a PC. Microsoft provides some documentation on the Audio APIs available to do this via a typical sound card, such as waveInStart, WaveInPrepareHeader, waveInAddBuffer and such like. I can lodge the names of my callback routines via Windows APIs such that I receive callbacks upon buffer-full interrupts on input and buffer empty interrupts on output. By keeping a couple of buffers in the I/O queues at all times, I can maintain a glitch-free flow of audio in real time.

But now I want to expand this to 4, maybe 8 or maybe 16 parallel input channels. I am looking at a TASCAM US1800 16-channel device which comes bundled with Steinberg software. However, I can find nothing about any APIs like the Window OS calls I mentioned above, that my software can hook into. I am not interested in recording. I take the audio in, process it, and push it straight out with maybe 100mS delay.

Can anybody point me to documentation that might be availAble from Steinberg or whoever on the audio driver APIs for a device like the TAsCAM US1800 or US1641 ?