How to override 2 (two) packages in Nixos configuration.nix

I have some package to override in my configuration.nix. So I write the code as follows:

nixpkgs.config = {
  allowUnfree = true;
  packageOverrides = {
    pkgs: rec {
      #mumble + pulse audio
      mumble = pkgs.mumble.override {
        pulseSupport = true;
      };

      #kernel for intel ethernet and Testing e1000e package override
      linuxPackages.e1000e = pkgs.linuxPackages.e1000e.overrideDerivation (attrs: {
        name = "e1000e-3.3.3-${config.boot.kernelPackages.kernel.version}";
        src = fetchurl {
          url = "https://www.dropbox.com/s/pxx883hx9763ygn/e1000e-3.3.3.tar.gz?dl=0";
          sha256 = "1s2w54927fsxg0f037h31g3qkajgn5jd0x3yi1chxsyckrcr0x80";
        };
      });
    };
  };
};

but when I do nixos-rebuild switch, I got the following error:

syntax error, unexpected ':', expecting '.' or '=', at 37,11

which is at pkgs: rec {...

What did I do wrong? At first I write it by separating the pkgs like this:

packageOverrides = {
  pkgs: with pkgs: {......}; #this is for mumble
  pkgs: rec {...}; #this is for kernel
};

and still got the same error.