But would need same gain....
No. If you adjust gain in the DSP domain it works perfectly with different gain in amp domain.
Here is the example of my system.
Each 8351b and JBL 128H woofer is crossed at 100hz, JBL uses seperate amp MM8077 and Genelec 8351b has -30dB switch on.
But with JRiver DSP individual volume control it works fine in all volumes.