Is SRAM Apex crankset compatible with 6 speed chain and rear cassette
Probably not as the Apex crank is designed for 10 speeds, a 6 speed chain will be too wide to fit onto the smaller chainring without jamming on the larger chainring. You would be OK using a 9 speed chain as they are pretty similar to 10 speed chaing in width. So sorry, you will need to up the number of speed front and back at the same time.