No you cannot especially on quad channel boards. The boards are suppose to support asynchronous timings but it's a recipe for disaster with the memory controller in the CPU. Also you don't want to get dual channel kits with quad channel boards. I suggest you get the same model and hope the current production has not changed chip manufactures on that model.
Viable/possible? Yes. Advisable? Absolutely not.
Are you at least attempting 2 more 8GB sticks for a total of 6 x 8GB or are you also mixing RAM stick sizes (4 x 8GB + 4 x 4GB)?
RAM has come a long way in the realm of compatibility, since the dark ages when chips of the same brand/model/spec wouldn't even work together (making you buy more expensive tested "matched pairs").
Worst case scenario, they simply don't work well together and your system is corrupted, OS needs repair or reinstall (along with eevverryything else).
Most likely scenario, especially seeing the timings (and potentially size per chip) differ, you will need to slow the RAM down even more than the ratings you have. You will probably need to disable quad channel. The slower you set your RAM, the more compatibility issues are smoothed. You may find yourself running 30+ on the total trip. With the performance loss, you may have more RAM but everything you do is just slightly smaller. Luckily with RAM this tends to be in the 1%-5% range, nothing extreme.
Unlikely but best case scenario, you can install the RAM and run it at the value brands speed (10-10-10-27). The faster RAM shouldn't have an issue slowing down but you will likely encounter issues if you attempt to run the value RAM at 9-9-9-24.
Corsair and RAM in general is so cheap, it's really worth just sticking with the same brand/speed. For the best dual/tri/quad channel support it's also best to stick with the same size per stick.
Thanks guys - I'll just spend a little more and buy the same kit that I currently have