As Bill said, just because paints use the same general solvent, or even binder, does not mean they are compatible. Acrylics slightly more so than enamels—but you find the same problem when trying to combine lacquers and enamels, for example. As a general rule, I never mix paints of different brands without testing for compatibility, first.
The compatibility of Gunze and Tamiya is possibly better than that of Tamiya and Model Master or PollyScale, but you will have to try each combination separately. I don't use Gunze—just a preference, I know people who won't use anything else. Both Gunze and Tamiya appear to have fairly complex formulations, but from what I recall, both are alcohol compatible (isopropyl, 90 percent).
To test compatibility, mix equal amounts of each paint in a small, glass, sealable container (old paint bottles, if thoroughly cleaned, are fine.) Thin them with a reducing solvent compatible with both. Let them sit for at least three days, then strain them. The results should be obvious—anything less than perfect mixtures without lumps or strings means that they are incompatible.