Here is another test:
On board nVIDIA nForce2 MCP-T soundcard, AC97, Realtek ALC 650/Asus Mb/Athlon-1.66GHz/Chipset nVIDIA nForce2-U400/XP+.
Home made tester at 6VDC.
The results before and after calibration show that nVIDIA nForce2 MCP-T is another on board good soundcard for I/Q.
@Stephan. I believe that every good card for I/Q can be almost "zeroed", it is a bit tricky to find the best adjustment combination but it is feasible...