Next thing is 2.5 Vs 4mm cable?? 😩🤔
That is correct - 2 core is what you need.
FYI, bi-amping is where you have two amps. Typically, but not always, one driving low frequency drivers, the other driving high frequency drivers. 4 core speaker cables allow you to feed both amplified signals with a single cable. As with most things, a quick google will explain things in more depth if you're bothered.
While there's no harm in using 4mm cable, it may make you feel more of a man. However, 2.5mm would be ample.
Net power loss will be minimal, as the cable is so short (presumably sub 1m)
This page explains in more detail, along with a cable size calculator tool.