Can I use TaqMan Assays if the stock concentration is only 20X?

Yes. When preparing assays for use in Dynamic Array IFCs, first combine equal volumes of 20X SNP Genotyping Assay mix and 2X Assay Loading Reagent, then add the recommended volume of 50X ROX™ Reference Dye. For example, the volume per inlet with overage would include 2.5 μL of 20X SNP Genotyping Assay mix, 2.5 μL of 2X Assay Loading Reagent and 0.25 μL of 50X ROX, for a total volume of 5.25 μL. Although the resulting assay concentration will be less than 10X, the chemistry is sufficiently robust to tolerate a slight reduction in concentration of all three components in the assay mixture.