TLS Guy tells me that group delay is what it is. I've seen other resources claiming that Hz * ms <= 400 is a worthwhile target to aim for. I'm afraid I don't have sufficient experience to confirm or refute either assessment. In this situation, though, I wouldn't put much consideration into how EQ and a subsonic filter affects group delay. Unless you've got bass traps and other acoustic treatments in your room, any room interactions will probably make the minutiae of group delay a moot point.
Consider that WinISD models anechoic response. With room gain, whatever rolloff you see will be much less pronounced. My sealed sub starts rolling off in the 40's; but with EQ house curve and corner loading,
Funkenspelunkin shakes my room and pressurizes my ears. Between your iNuke's DSP and your miniDSP, I think you've got the response curve covered. You might as well go with the smaller enclosure.