The crossover and tone controls built into the head unit just doesn't cut it for a true SQ system. You'll want to run your morel components active (without the passive crossover) so you can adjust crossover points and slopes from your DSP. This will give you maximum control over your sound.

You can do better than Morel subs for the price. Image Dynamics makes great SQ subs. The IDQ series is a great sub at a relatively low price compared to Morel and the performance is much better. There are many others out there but the key is all in the tuning.