any users of the signals&systems package? how to find Discrete Time Fourier Series?

Hi;

Any one here uses the Mathematica Signals & Systems package?

I am unable to find how to determine the DTFS.

For example, this is a periodic, discrete signal, that has
a period of 6 samples.

x[n]:= Cos[Pi n/3];


The closest function I could find is to call DFT (even though
this signal does not belong to this class), then divide
the result by 6 (the period), but this does not give
the correct result.

Needs["SignalProcessing`"];
x[n_] := Cos[ Pi n/3];
M := 6;
seq = DiscreteFourierTransform[x[n], M, n, k];
func = TransformFunction[seq];
func = (1/M) func[[2, 1]]

The result is {0,1/6,0,1/6,0}

while the correct result should be {0,1/2,0,0,0,1/2}

I have tried this on other signals and I can't get
the correct result on any one them.

any one using this package can show me how to do this?

thank you,
nospam