I am attempting to bi-amp my 70's with the left and right channel of an Adcom GFA-7500(150wpc x 5) for the highs and an Adcom GFA-565(300wpc mono,dual spkr outputs) for the lows. I have checked my wiring 10 times over. With jumpers in place and only the 7500 running hi's and lows, they sound very good. Remove jumpers and add 565 to the lows.The hi's(drivin by 7500) all but dissappear. Same setup/experiment with my NHT VT-2's works flawlessly both ways. Only major diff being 6ohms nominal on NHT's and 8ohms on polks. Any idea's?