2-channel listening with a sub-woofer


Is anyone using a subwoofer for 2-channel listening? Have you ever heard a subwoofer for 2-channel listening?

If so, did the sub integrate seamlessly with the speakers? What sub was it?

When using a subwoofer, is it no longer important for the 2-channel amp to be able to drive the woofers?

For 2-channel, is a sub with a 15 inch driver faster than one with an 18 inch driver?

(say a 15 inch Velodyne DD vs an 18 inch Velodyne DD.
128x128mitch4t
I get seamless integration, but the sub and speakers are from the same company.
"have you ever heard a subwoofer for 2 channel listening" sorry but that sounds funny... people have been using subwoofers with stereo systems for 30 years or more... Dalquist, Velodyne, Janus, JBL (and others) all had subwoofer products in the 70's. The famous Beverage speakers came with a pair of subwoofers.
Xiekitchen, I'm aware they've been around a long time...I've just never heard one myself in a high end 2- channel setup...and the overwhelming majority of the 2 channel systems that I've seen posted here on the 'Gon don't run a sub.

I'm considering a purchase of a sub for my system.

Back to my original question...have you ever heard a sub in a 2-channel system? How did it sound and was the integration seamless? What type of sub and speakers were used?
I'm running a Rel Storm III with Totem Mani-2's and it integrates perfectly. I previously ran the Rel with Totem Sttaf's (prior to upgrading to Mani) and it was also a beautiful combination. The Mani's have much deeper bass than Sttafs so the sub is less necessary. Finally I also had a Rel Storm I set up with GMA Europas. A sub with the Europas is essential IMO.

My point is all 3 above setups were stereo, integration IMO was perfect and somewhat simple (though somewhat harder to set up with the Europas). For the Europas the x-over was at 49Hz, Sttafs at 38Hz, Mani-2s at 28Hz. In all 3 cases the soundstage is bigger, imaging at least as good.