Addin Worksheet Function In VBA

I have found an addin (http://www.quantdec.com/Excel/smoothing.htm) that adds a worksheet function smoothing data. It operates with 2 arguments:
- a range for the input data to smooth
- a parameter detailing how to do the smoothing.

It outputs a matrix of smoothed results, and therefore requires the Ctrl-Shift-Enter on a spreadsheet. Until there no problem, the function works properly. However I need to repeat the process about 100 times. Therefore I extended my ranges to duplicate the calculations, and that also worked fine. But because I don't need the intermediate data (100 columns by 1000+ rows) and I don't like to wait 2 minutes for the calculations to finish each time I open the saved file again, I thought I could just use VBA and only output the final results.

This is how the working syntax is in a cell:
=SMOOTH(B3:B1032, "5RSSH,5RSSH,>,5RSSH")

And there the nightmare starts :
- I cannot apply it even once: I get a type mismatch whatever I do to calculate the range and put it as an argument of the function. I used a string to store the range name and use it as is (B3:B1032 or even "B3:B1032") or with the Range function Range("B3:B1032"). I even tried to put manually "B3:B1032" with the same result. First major issue

- Because the worksheet function requires a range, I cannot use an array, or at least I tried without success. Therefore I need to output the result on the worksheet each time it is processed, and reread it through the formula, for n times the loop is running for... Kind of inconvenient... So I tried to modify the original smooth() function to create a new one that would accept an array as argument instead of range, but with the same consequence: Type mismatch when I feed the new function with an array (which I checked contains the data to process).

I have tried an example I found somewhere using a built-in Excel Worksheet function MMult and it worked with ranges:

Sub SomeSub()

Dim xArray As Variant, yArray As Variant, zArray As Variant
Dim Fn As Object
Set Fn = Application.WorksheetFunction

xArray = Range("A1:B2").Value
yArray = Range("D1:E2").Value
zArray = Fn.MMult(xArray, yArray)

ActiveCell.Resize(2, 2).Value = zArray

End Sub