2 Pre-Outs?

I have a high end preamplifier (which has 2 balanced pre outputs) connected to two stereo amplifiers, both J. Rowlands 112's. Each amp is connected two a pair of 8 Ohms loudspeakers with fairly equal efficiency ratings.
When I play a source (digital or analog) both loudspeakers lose their inherent sonic virtues, particularly gain. When I play each one individually(by turning off one or the other amp.), each pair performs flawlessly.
Should I increase the gain on the preamp?
Without actually seeing how you've got things hooked up, my first thought is that somehow or other, one amp-and-pair-of-speakers combo got connected out of phase to the other group.
Are you stacking?
Most speakers will not sound good played simultaneously with annother pair.
Most speakers introduce their own phase shifts throughout the spectrum. It would be rare that two models, from two different manufacturers, with two different efficencies would have the same phase shifting characteristics. Regardless of phase going into the speakers you are hearing serious cancelation.

Good luck!
I have done experiments with 2 pairs of speakers playing together before. It can work but you have to really REALLY work at getting them in the right spots so as to not get wave interference - which sounds to me is the problem you are having. In my experience, just half an inch of toe-in can make or break it. If you have them close to each other, it will be much easier. I don't think your preamp is the issue - just speaker placement and/or compatibility.

It is doable of course, otherwise home theater would be a crock of s, but stereo imaging demands much more accuracy in your speaker placement.
There is a large difference between home theater/surround sound and two pairs of speakers simply playing the same information. HT involves intentional differences in phase and timing for matrixed surround sound and discrete channels of information for DVD's.

Otherwise we could simply use the B-speaker outputs of a stereo receiver to surround ourselves with sound.
The difference in phase is what we are talking about, just like you said in both of your posts. Also, the difference isn't large at all - it all comes down to playing with just a few milliseconds.

Using the B-speaker outputs works very well for surrounding yourself with sound. I don't know if you have actually tried it but I have and it sounds rather realistic if you get the positioning right.

Of course, I am only talking about music, like Drmoles is, so you can't expect there to be any sort of "decoding" needed - just a few milliseconds delay to create a feeling of ambient space and that is pretty easy to do.
I'm a bit confused. Are you passively bi-amping one pair of speakers, or, are you simutaneously running two pairs of speakers?
I agree that cancellation and phase variations are at work. 2 outputs are generally used when bi-amping or running 2 rooms... I have stacked 2 pairs (years ago) and achieved ok results but ultimately what you are trying is an '80's idea. Using a 2nd pair of back speakers (with much reduced volume) to produce 'ambience' and 'space'. Running both pairs at matching volume is very hard to pull off.
Well guys! Call me crazy if you want, but at the present I am running 3 systems at once; yes, 3.
3 Preamplifiers, 3 amplifiers & 3 pairs of loudspeakers.
All the loudspeakers have a different positive as well as a negative sound quality to it.
One system consists of a Jeff Rowland Concerto Preamplifier, A Jeff Rowland 112 Amp hooked to JM Labs 937 BE Anniversary Edition.
The second system is a Jeff Rowland Consummate Preamplifier, a Jeff Rowland 112 amplifier hooked two a pair of Aestheth VI Elite Loudspeakers.
The Third system consists of a Antique Sound Labs Otl 32 preamp (also can double as headphone preamp), a Cary V12i Amplifier (running in triode mode) hooked to a pair of System Audio 1532 Loudspeakers.
All sources are daisy chained thru the systems with Crystal Cable, Loudspeakers use Soundstring Cables.
I am using the 2 outputs of a Cayin SACD player.
I can play each sytem separately or all played at once at different gain levels.
I have failed to notice any Phase problems.
So, call me crazy since it sound like a derranged idea. But I call it Synergistic sound arrangement like in a good and well tempered choir.
By the way, I did not have to spend the money on a pair of Wilson Alexandrias or Grand Slamms and other exotic sound gear.
This sounds like a Rube Goldberg project. :)

Seriously, along with the issues previously mentioned I'm wondering if there is something going on with the sensitivity between pre and amps when you try to run everything together. Don't know where you're trying to get to, but have fun.
Hi Dan_Ed:
I am been searching for performance level reproduction (96 dB's without fatigue and stridence) and I think that I have achive room filling sound that is involving, accurate and quite detailed.
I'm sure it's filling the room! :) As to gain, if the pre is built to run both outputs simultaneously I would not expect there to be any issues with gain. Do you find that when you drive both amp/speaker pairs that you have to double the volume setting to get back to the sound of a single pair?
Drmoles,What you are doing is truly radical.I do know a bloke who uses a pair of Quad 989s along side some Infinity ribbons and active woofers-through different power amps so I guess this is similar.He reckons this just really works well.So maybe you are on to something.
Take a look at my "system" page. I did the same with 2 systems. Enjoy!
Hi Aball:
That is one impressive set up, done with taste, a sense of balance and Musicality in mind.