Bi-Amp w/Sub Amp Setup

Looking for insight on this topic.  I have  NHT 3.3 speakers with separate speaker inputs for the Woofer (12" Driver in the sealed chamber), and inputs for the upper-end Mid/Tweeter array.  I come off my Preamp into the Sub Amp (NHT SA2) line level, and then line level from the AMP Out to the 2nd AMP (Tube Amp) to drive the Mid/Tweeter array on the 3.3.  I follow the suggestions for settings of the SA2 crossover/HI & LOW Pass, but struggle with the best way to measure that the variable volume/gain on the SA2 is set to best match/integrate the upper and lower end of these speakers.  Here is the detail of my work - done per the instructions.  Should I separately test the upper end with a 150 or 300hz signal for SPL, and then only connect the lower end with a 60hz signal and assure they are the same SPL?  That has delivered - mixed results.  Curious as to other recommendations for optimal integration.  Many thanks for reading and the help.