Stereo subs is the way to go. However, it requires more effort in initial setup. I am using stereo Sunfire Signature subs with my MG 3.5 (I am also biamping with a Marchand XM126s) Blend is seamless. All musical parameters have been improved (caution: go easy on the voume control).
Depending on the frequency response of your main speakers, use the lowest x-over point possible.
Depending on the frequency response of your main speakers, use the lowest x-over point possible.