Setting up dual subwoofers to a two channel amp.

In addition, would I be correct in describing the alternative method you mentioned as having two sets of wires running from one set of speaker posts on my SET? One set to the full rangers and one set to the speaker input of the sub amp?

"Does this method we are talking about have a bad effect on the full range sound?"

IMO, No if you can get it set up properly. Possible issues that may come up are; any overlap of the main speakers and subs as well as phase issues at the crossover point.

"Also, does adding a sub in the manner we are describing make the main amp work harder than if there were no subs at all?"

No. What I was talking about is in a true biamp set up (active crossover before the amps and sub's) I'd be removing the deep bass, below the crossover point, from the main amps. Simply put this would remove some of the demands on the amp since the bass requires much more power than the mids and highs do. My main speakers would also perform better as they would no longer be asked to do the deep bass.
The system would be able to play louder with less distortion. However in my case the quality of the mids and highs are negatively impacted by all of the active crossovers that I have tried so far. So I am running the SET amp and main speakers full range and using subs to augment the bass the main speakers can't do. After much "dialing in" the set up I am very happy.

This is all great info. Thanks so much!

I had a 2.2 set up with a single driver speaker, matching subs, and a 300b set amp. I ran direct from the amp to the main speaker then a jumper from the main speaker to the powered subs. I tried to dial in the subs as best as possible, but had nulls and phase issues at the crossover point that Jjrenman referred to.
I have since gotten away from horns and have a 2.2 set up using monitors and matching subs with a Dspeaker Antimode Dual Core 2.0. In reality you have an active system with each channel having it's own dedicated amp. Which will only need to provide enough power to run the driver to full excursion. Very smart for good sound!
I use my Dual Core as a preamp and dac with a transport to the internal dac. There are 2 digital inputs, optical SPDIF and USB, XLR and RCA analog inputs, with XLR and RCA outs.

So how will this work for you?

With the Dual Core you can measure the room and see where your horns begin to drop off and set your subs crossovers accordingly.
ie: My monitors drop off steeply at 100hz. I use a XLR to RCA cable from the XLR out to a single ended amp for the monitors. Then from the RCA outs to the subs amps dialed in at 100hz. I Then run a room correction at 150hz (or which ever point you want to choose up to 500hz) which fixes room nulls, and phase issues, as well as correcting the crossover point. The Dual Core's algorithm is so good that if you miss the proper crossover point by a few hz, it will make adjustments to bring the frequencies to proper alignment.

The Dual Core are around $1100.00 and will give you the great sub to speaker integration, as well as tone controls, equalizer, room measuring, tilt and house controls, up to 4 different profiles to save corrections in, asynchronous USB input, optical digital out, and support fron Dspeaker for future firm ware updates.

Oh by the way the Dual Core is responsible for the best bass and over all sound I have ever had in my room. ALSO *I'm not affiliated with Dspeaker in any way other than a very pleased customer.*

Dspeaker Dual Core

http://www.simplifiaudio.com/online_store/dspeaker_store.html

Use an active pre-amp (SS is better than SET for bass response) with 2 RCA outputs to split the signal from the CD player/Media player/TT two ways - one direct to your 300B and then the Horns, 2nd using Y splitter further to drive each plate amp/subwoofer

My system is now PWD DAC II (has XLR and RCA both with active signal) - XLR to main preamp - 45 tube active and to my AN300 B monoblocks; RCA with splitter ie 2 lefts to left subwoofer bridged amp and 2 rights to right bridged subwoofer amp. Separate volume on PWD DAC, Tube Main Preamp, and adjustable X-over frequency and Volume on Subwoofer amps makes adjustment and blending seamless.