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.
Yes. Mixed results. Saw it coming a mile away.

Connect the pre-amp to the tube amp to the speakers. If there's a jumper involved then go direct to the uppers and jump to the woofer. Click on over to the for sale section, post all the bi-amp crossover stuff. When it sells, buy Total Contact, Orange Fuse, ECT, and HFT, in that order. That should keep you happy for a while. Unlike bi-amping, which is tailor made for making people frustrated ... and poor.
Just looking to understand your original question. Have you set the SA2 column and done a sweep across 20-20K?

Also- do you have a 2nd line out on the preamp? If so, have you thought about running a separate line out from pre directly to your tube amp for the upper section (and bypass the in/out on the SA2)?