One or two subwoofers?

Invisibility and blending are a function of crossover point, slope, type of crossover (level matching & damping controls), number of subwoofers and (last but not least) matching tonality of subwoofer and woofer drivers. I have paid attention to all these and I get perfect blending and invisibility between 4" woofers and 10" stereo subwoofers using a modded Marchand electronic x-over.

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.

I'm running three subs, one from my pre-pro's LFE out and two from an extra set of pre-outs. I use an outboard crossover for the stereo pair set at 35hz and run my mains full range. The third sub only comes into play for movies.

Dave

I have a pair of Dunlavy SC-IV speakers, which are supposed to go as low as 30 Hz. I had a REL Stentor III for home trial. I dialed the setting for the high pass filter in at 25 Hz., so it has to be low enough to be non directional. Does anyone have experience with this combination? It's of course also a matter of costs: one Stentor III is already expensive, but two of them is very expensive! But I wonder: would one Stentor III not be enough to make a good sound?

Dazzdax

One sub will be fine for you. Here is a link to some subwoofer info. http://www.soundstage.com/maxdb/maxdb021999.htm

Dave