Using sliders with Lab color?

Take a look at Indigo Ray's CMYK snippet. Maybe that would help (unless that what you mean by "adding modules for each channel, making inverted duplicates of each, and adding a blend (with int slider) between each pair", in which case forget about it).

As far as I know it's much easier to convert RGB to CMYK and vice versa, since both are physical representation of light (They are actually the opposite of eachother).
LAB color however, is a mathematical representation of color. It only exists in computers. Therefore the conversion is purely mathematical.

If you want to get geekier, read on. Otherwise run away
Color is actually mixture of different light wavelengths. White light (Like we get from the sun) is a mix off all the colors of the rainbow - Red, orange, yellow, green, blue and violet (And a whole lot of other wavelength that we can't see, like Infra Red and Ultra Violet). You can also create white light by just mixing Red, Green and Blue lights, which are additive colors (Meaning they add light to eachother). That's how TV's and Screens work. They EMIT light.
CMYK colors however, are substractive colors. That means they SWALLOW parts of the white light, and the colors we see are the "leftovers" that were able to bounce off from the surface to our eyes. White means no light was absorbed, Black means no light was able to escape, and all the light was absorbed. The CMYK colors (Cyan, Magenta, Yellow and blacK) are used in print, in which case you take a white paper that doesn't absorb light, and make it absorb differen wavelengths by printing on it.
Each color space (RGB, CMYK, LAB) has different color properties. CMYK has the least amount of colors. RGB can show colors on screen that won't print on CMYK, because it's a wider color space. LAB color space has much more color than RGB and CMYK. In fact, so much color, that neither the human eye, nor screens and printers can interpret all of it. That means some colors in the LAB space are "theoretical" colors. They can't be recreated in the physical world.

They must beairing too many coocking shows on TV....