Monitor close to the wall to replace Allison 4s

Yogiboy, I am really just doubling the output to each speaker currently by sending both left channel outputs from the preamp (there are 2 sets of outputs to the amp, of course) to the left stereo amp and sending all the output of the left amp to the left speaker and vice versa to the right speaker. Isn't that what vertical biamping means, even though one amp feeds one speaker? Advantage? Double tube power to each speaker.

Yogiboy, you are correct semantically, it is not "biamping" - Eldartford in a thread on vertical biamping calls what I am doing "Dualamping". Better?:)
Do you follow my aim and are there technical problems with it? It certainly works and sounds a lot better than when I use 1 amp conventionally.

Anybody try the Kef ls50s against the wall?

Denis- they had a pair of Clue's for each channel, stacked one on top of each other, w a dedicated stand or spacer between the two, w the top speaker upside down so you got a quasi-D'Appolitto array. Woofer-tweeter-spacer-tweeter-woofer. They were set up on the long wall of a narrow hotel room, w two rows of seating about 8-10' away. I thought the sound was very dynamic w great PRAT. They are designed to be 2.5" or less from wall w significant toe in.

"I am vertically bi-amping, one amp per speaker, so I could just double up the cables on each speaker. Any reason not to?"

Yes, IMO, there are reasons not to.

What you are referring to amounts to paralleling (aka monostrapping) the outputs of the two channels of each amplifier (i.e., connecting them directly together, through the speaker cables), with the same signal going into those two channels. As Yogiboy indicates, that is completely different than passive biamping, which is what you are presently doing with the Allisons (and which is what ElDartford refers to as dual-amping, to distinguish it from active biamping).

Passive vertical biamping, as you are doing now, results in one amplifier channel supplying current and power essentially just at mid and high frequencies, and the other amplifier channel supplying current and power essentially just at low frequencies. Paralleling channels is completely different, and results in both channels supplying current and power at all of the frequencies that are contained in the music.

Paralleling amplifier channels CAN be done with many tube amps (don't ever try it with a solid state amp!!!), and it can provide a considerable increase in power capability. But if things go wrong there are ways in which it can have very destructive results. And it is likely to produce very different sonic results than either passive or active biamping. And for good sonic results it would most likely necessitate changing which output taps on the amplifier are being used, and in some cases it may turn out that none of the available taps are optimal.

See the post by Atmasphere dated 2-11-13 here, and the discussion by Atmasphere and me in this thread.

I'll close by mentioning one conceivable scenario that to ME is sufficient reason in itself to avoid ever paralleling two amplifier channels: A small signal tube serving one channel of the amp fails, at some point in the future. You start playing music. One channel is trying to put many volts and watts into the speaker, while the other channel (with the dead tube) is trying to force the speaker's input to zero volts. The outputs of the two channels are, of course, connected directly together through the speaker cables in that situation. Ouch!

Regards,
-- Al