Convert CMYK+SPOT (only selected bands) to RGB

Hello,
My context:
I am dealing with multi-band TIFF files - CMYK + one or more SPOT colors.
I am able to read the multi-band TIFF file using JAI and read the number of bands correctly.
Also, I can read the value for any band for any pixel.
For the SPOT colors I have Pantone CMYK equivalents.
The bands are 8 bit in size.
My problem:
I need to be able to show/hide one or more bands and display the result.
Is there a (mathematical) formula for converting CMYK+SPOT color bands to the RGB color space?
A simple example:
(CMYK scale 0-100)
All bands: C, M, Y, K, SPOT1 (C=100,M=100,Y=0,K=0), SPOT2(C=100,M=0,Y=100,K=0)
Bands selected: C, M, SPOT1
PixelX values: C = 50, M = 10, SPOT1=80
Can we calculate PixelX's RGB values to display on screen?
Is there any documentation I can read anywhere on the subject?
Thanks in advance,
Georgi

While I have never tried it, you might find this interesting: [cmyk to rgb|http://bytes.com/topic/java/answers/16180-rgb-cmyk].

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