You buying the sealed flatpacks with the driver or building ported boxes or ?
Not sure how you figure the XLS crossover will help you integrate the subs, the minidsp sure (or even just Audyssey can do a reasonable job, and as you can utilize the app even limit its eq to the bass frequencies/below schroeder). The XLS dsp is really more intended for crossover work, and not with an avr involved.
At first I was putting a bridged 1500 on each of my SI HT18D2 DIY sealed subs, but figured with the levels I needed to play back at (I generally do around -20dB, sometimes up to -10dB) one channel on each amp was just fine long term. You'd only lose what 1.5 dB from the XLS 1502 to the 1002 but I'd generally aim at the 15xx and up just because of the slightly better snr spec. Just a matter of the right tool for the job in the end, tho.