upgrading stereo system

02' 4dr. golf stock radio dbl din moonson.Installing a new HU, amp, and sub. I will run separate line to power the amp but still want to use the stock speakers for now.In the future I want to put a 4 channel amp and a new component system mid speakers, dont want to route new wire to the doors, is it possible to use the existing wire coming out from the moonson amp, which is by the way going to be deleted.Please help!!!?.