Powered subwoofer and phase inverted preamp

I had an integrated amp and had line out to powered sub.

Now I have preamp with main outs to power amp. I must use the speaker outs from amp to speaker ins on sub. Do you just overlap the speaker wire on the amp? I use bare wire. Also, the preamp is phase inverted. Will that cause a problem with the polarity of the subwoofer or the main speakers?

It depends on your room and system. My RELs have a phase inversion switch and advise that the correct position will depend on individual conditions. Just overlap the wires or use bare wire to the mains and use a banana plug to connect the sub signal if you have the 5 way posts, I do that.
If you want to restore normal polarity wire the speakers and sub with amp hot to speaker ground (or vice versa). You can reverse the polarity of the sub by wireing it in the usual manner, hot to hot etc. You can check to see which wireing is better for the sub in YOUR room.