CPU is probably not the culprit imho, but if you say CPU = 100%, check first if this is indeed the CPU and not the asio (monitor) driver who is at 100%.
If it is the asio driver that fails:
Pinning down a system who is underperforming is not easy. It can be not enough memory (you need at least 4 gig minimum), it can be buss-speed (can not reach the CPU in time), a slow harddrive (can not reach the CPU in time), and so on.
If it is in fact the CPU and nothing else (see taskmgr)
- lower bitrates and sampling frequencies. The CPU can not handle the task.
good luck on tracking the issue
kind regards,
R.