Have a read of this:
The length recommendation is for Naim speaker cable. It’s possible that the optimum for other cables is even longer, but if they don’t publish inductance and capacitance figures, it’s not so easy to make an informed choice.
I wouldn’t worry too much about this, your 200 will not explode! The worst that might happen is that it could run a little warmer if pushed hard, and it may sound a little better with the correct spec and length of cables, but I wouldn’t let that stop you from using what you’ve got.