Trouble shooting these type of issues can be frustrating. Are you and your brother using the same Windows operating system? The speaker package should theoretically be just fine. However, some can give you a headache due to their design. I assume you've tried different drivers just in case to rule out any OS bugs.

Otherwise, I haven't encountered any issues here using some basic Creative and Altec 5.1 speaker packages on the P55 or P55A motherboards that have the ALC889A Codec.