The thing about these "captures" is that they captures a single setting of the amp (or whole signal chain), whichever was set at the time of the capture. So, there is no real "gain" or EQ that would mimic the real amp. You might as well use your favorite EQ plugin after the it (or before, but it will likely be more subtle) and some pedal emulation before it to increase the gain. To decrease, you can try to lower the input volume, but that is not ideal, as it is more like turning the volume down on your guitar.
So, I don't really have a problem with no controls, as it gives you what it is really supposed to... It works great as is, and with a pedal and EQ you can get some flexibility from a single capture.
Just my 2 cents.