I would not recommend using combinations of random single modules. There is no guarantee that such combinations will work.
The FX-6300 supports 1866MHz speed. I would check your BIOS settings for:
Set Memory Clock to [Manual]
Check what Memory Clock options are available with the FX-6300.
X8.00, 800MHz, 1600MHz settings
X9.33, 933MHz, 1866MHz settings
Purchase a kit with a matched pair of either 1600MHz or 1866MHz depending on what Memory Clock options you have available in the BIOS.
Also set DDR3 Timing items to manual.
Set the CAS# Latency number to memory specs. This is the first Timing number.
Set the next two or three numbers to memory specs.
For example:
DDR3 1600 (PC3 12800)
• Timing 9-9-9-24
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231416