Re: Kernel 2.6.26-rc6-custom compile with .config from stock kernel: ALSA config miss
I've seen the same thing when building a custom kernel and using an Ubuntu kernel config as the base. My guess is that it's important enough to have up to date alsa and wifi drivers that they build them outside the source tree and just include those modules in the kernel. In fact, you can do the exact same thing without having to rebuild the kernel if you want.
Don't try to make something "fast" until you are able to quantify "slow".