Limiting a full range driver

I am considering a miniDSP SHD Studio, all digital with no converting to analog, and then sending out to 2 DACs (OKTO DAC 8 to main speakers / Schiit Modius to my 2 15" passive subs). Amplifiers are Benchmark AHB2 for mains and a Crown Class D (750 WPC) to the subs. All on AES/EBU and balanced.

Well, the usual recommendation to avoid subwoofer localization and enhance the ability to put it elsewhere is to keep the low pass filter somewhere below 120 Hz.  I haven't heard any other methods.

OP:  Sounds like a good idea, but, this is key, be ready to measure your results.  Once a speaker/subwoofer gets into a room throw the specs out the window and pretend you know nothing about the performance of the speaker, because without measurements you really don't.  The room changes everything so while I think your approach to using digital miniDSPs is sound I also think you'll need to carefully gauge the setting and for that you'll need a mic and software.

It's an 8" driver and it can handle but low frequencies without distress.  If you really want to set a low limit you should aim for a 60Hz or less.  Do you really want your 15" subs handling the upper bass region?

I plan on getting the UMIK-2 (the better one) because the miniDSP also has Dirac that will need measurements. I know the 8" can handle the lows, but does that prohibit the midrange from sounding its best?