Hi all. This is my first post. Currently I have a Harman Kardon 2 ch stereo reciever-75X2 RMS with a pair of Polk T15s and Infinity 10" 150 watt sub. I plan on getting a pair of TSi400s and more power-maybe about 150 per speaker. Will the sub still be needed? With that much power going to the 400s, will the sub even add anything to the system? Thanks in advance.