Is SRAM Apex crankset compatible with 6 speed chain and rear cassette My bike's parts are in need of change and I wanted to do this in stages.

Currently it has shimano parts based on a triple mountian bike front crank and derailleur and six speed rear cassette and derailleur.

First part of the plan is to update the crankset to a SRAM Apex double 50/34 cranks.  So will this crankset be able to use a six speed chain connected to the rear cassette.

As a side I have confirmed with SRAM directly that their road gear is 100 % compatible with their mountian bike gear so my plan is to mix and match the Apex front end with X5 rear end equipement but I can only do this in stages.
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.