L2 cache is detected on my QX9650 on bioses 2506 and newer (2406 and 2302, the earliest that supported QX, showed 0k, BUT Sandra, CPU-Z and Everest showed the proper cache (and the cache/memory speed test functioned as it should).

If you're getting 0k in 2801 with the Q9550, you should still at least get the proper size in CPU-Z. If you're getting 0k in cpu-z too, can you run an everest memory benchmark and look at the speeds of the L1 and L2 cache?