This also largely depends on your hardware and your kernel. If the hardware has no physical means to handle all the input then no OS will help with that. There are a number of factors that can influence this. So make sure that:
- that dma is o for all your drives
- that there's no background task wasting cpu time
- you record raw (no compression or processing in the fly, less cpu power needed)
- you use jack and no preemption in your kernel if you still can't get good results
- you try a simple program like sox which will not waste so much cpu in other tasks
Sorry if this is way to trivial or if you already tried some or all of these, but you really gave not so much info. Knowing your kernel version, distro, what did you try, if your kernel uses preemption or any real time patch cruft or something can also be an important thing to know.
