I did some reacher on ohms and that just confused me even more

. So dont flame me if this topic has been discussed before.
Ok, I have a Kenwood Vintage amp (2ch) and speaker. It does speakers A "or" B at 8 ohms and A "and" B at 8 16 ohms. What i want to do is connect a sub to it. If i use both A and B i will be getting 16 ohms. I want to custom build a sub usuing the Dayton SA240 240W Subwoofer Amplifier for the sub. which is 4 ohms. Im trying to figure out how much ohms will the sub receive. So the kenwood amp will send 16ohms to the 4 ohm sub amp and then how much will the sub amp send to the driver.
The sub amp plate also has two output channels, so if i were to connect two more speakers to the system how much ohms will they receive?
This is asking for a lot and i would really appreciate it if someone could point me in the rite direction.