Can I mix 8gb ram with 2x4gb?

[gjataredi]

I ordered a pc with 1x8gb (3200mhz, 16CL) ram just because I didn't have the option to choose 2x4 and of course the money to order it with 2x8gb. Anyway now I want to add this 8gb so it will work dual channel. The problem is that I can't find anywhere a corsair vengeance ddr4 1x8gb cl16 3200mhz. I can only find these specs on 2x4gb. So my question is: Can I add these two sticks and still get the dual channel mode plus the 8gb like extra ram?
(uhm.. I can find one 8gb 2666mhz. Is it going to work dual channel? Even if they both work at 2400 for example?)
I know I may sound newbie but this happens only because I am .
Thank you in advace.

 

[jojesa]

For dual channel to work it needs memory modules in pairs, so you should go with a similar module (1x8gb, 3200mhz, 16CL).