You really have to do it by ear, use 60-70 hz as a starting point on the sub. I would not filter the output on the D7050 in the first instance.
Listen to see what position gives the best transition,you are looking to get to that point where you don't really hear the sub at all, just your speakers sounding 'bigger'.
Once you have decided on the best settings, note them down then try with the rolloff on the sub set to it's highest frequency (150hz ?) and adjust the rolloff on the amp. It may give you a different effect.