Is there a way to mix these memory modules?

I'm trying to mix two 4Gb DDR3 modules from G.Skill with another two 4Gb DDR3 from a generic Chinese brand called Ankowall. The BIOS detects all modules and automatically clocks them at 1333MHz but neither 64bit (Linux & Windows 10) nor memtest 86+ detect the 16Gb, only 8Gb. I've tried all combinations, testing each module and any combination of them in each slot. I've tried mixing a G.Skill module with an Ankowall module. They are compatible between different brands and the OSes detect the 8Gb no problem, clocking the modules at 1333MHz with no problems. But as soon as I plug another two modules the OSes don't detect more than 8Gb in any combination. So the problem seems to be with quad channel configuration maybe? I've also tried to force 1333MHz and 1066MHz in the BIOS, setting the memory voltage, the primary timings and secondary timings to no avail. Checked all the timings were correct in HWInfo64. I haven't tweaked the CPU values in the BIOS My CPU: INTEL i7-2600K My mobo:ASUS Maximus IV ExtremeZ Mem: Ankowall modules Here's the output of two memory diagnostics commands: dmidecode -t memory # dmidecode 3.2 Getting SMBIOS data from sysfs. SMBIOS 2.6 present. Handle 0x0060, DMI type 16, 15 bytes Physical Memory Array Location: System Board Or Motherboard Use: System Memory Error Correction Type: None Maximum Capacity: 32 GB Error Information Handle: 0x0062 Number Of Devices: 4 Handle 0x005F, DMI type 17, 28 bytes Memory Device Array Handle: 0x0060 Error Information Handle: 0x0064 Total Width: 64 bits Data Width: 64 bits Size: No Module Installed Form Factor: DIMM Set: None Locator: ChannelA-DIMM0 Bank Locator: BANK 0 Type: DDR3 Type Detail: Synchronous Speed: 1333 MT/s Manufacturer: 0080 Serial Number: 7A0F265B Asset Tag: 9876543210 Part Number: ANKOWALL Rank: 2 Handle 0x0061, DMI type 17, 28 bytes Memory Device Array Handle: 0x0060 Error Information Handle: No Error Total Width: 64 bits Data Width: 64 bits Size: 4096 MB Form Factor: DIMM Set: None Locator: ChannelA-DIMM1 Bank Locator: BANK 1 Type: DDR3 Type Detail: Synchronous Speed: 1333 MT/s Manufacturer: 04CD Serial Number: 00000000 Asset Tag: 9876543210 Part Number: F3-17600CL9-4GBXLD Rank: 2 Handle 0x0066, DMI type 17, 28 bytes Memory Device Array Handle: 0x0060 Error Information Handle: 0x0065 Total Width: 64 bits Data Width: 64 bits Size: No Module Installed Form Factor: DIMM Set: None Locator: ChannelB-DIMM0 Bank Locator: BANK 2 Type: DDR3 Type Detail: Synchronous Speed: 1333 MT/s Manufacturer: 0080 Serial Number: 7A0F265A Asset Tag: 9876543210 Part Number: ANKOWALL Rank: 2 Handle 0x0068, DMI type 17, 28 bytes Memory Device Array Handle: 0x0060 Error Information Handle: No Error Total Width: 64 bits Data Width: 64 bits Size: 4096 MB Form Factor: DIMM Set: None Locator: ChannelB-DIMM1 Bank Locator: BANK 3 Type: DDR3 Type Detail: Synchronous Speed: 1333 MT/s Manufacturer: 04CD Serial Number: 00000000 Asset Tag: 9876543210 Part Number: F3-17600CL9-4GBXLD Rank: 2 And lshw -class memory *-firmware description: BIOS vendor: American Megatrends Inc. physical id: 0 version: 3603 date: 11/09/2012 size: 64KiB capacity: 8MiB capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer acpi usb biosbootspecification *-cache:0 description: L1 cache physical id: 5 slot: L1-Cache size: 256KiB capacity: 256KiB capabilities: internal write-back unified configuration: level=1 *-cache:1 description: L2 cache physical id: 6 slot: L2-Cache size: 1MiB capacity: 1MiB capabilities: internal varies unified configuration: level=2 *-cache:2 DISABLED description: L3 cache physical id: 7 slot: L3-Cache size: 8MiB capacity: 8MiB capabilities: internal unified configuration: level=3 *-memory description: System Memory physical id: 60 slot: System board or motherboard size: 8GiB *-bank:0 description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns) [empty] product: ANKOWALL vendor: 0080 physical id: 0 serial: 7A0F265B slot: ChannelA-DIMM0 width: 64 bits clock: 1333MHz (0.8ns) *-bank:1 description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns) product: F3-17600CL9-4GBXLD vendor: Fujitsu physical id: 1 serial: 00000000 slot: ChannelA-DIMM1 size: 4GiB width: 64 bits clock: 1333MHz (0.8ns) *-bank:2 description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns) [empty] product: ANKOWALL vendor: 0080 physical id: 2 serial: 7A0F265A slot: ChannelB-DIMM0 width: 64 bits clock: 1333MHz (0.8ns) *-bank:3 description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns) product: F3-17600CL9-4GBXLD vendor: Fujitsu physical id: 3 serial: 00000000 slot: ChannelB-DIMM1 size: 4GiB width: 64 bits clock: 1333MHz (0.8ns)