Do I need BOTH amp and pre to be sonic holography?

The delay that Carver's holography unit developed was not just to somewhat counteract the signal from the opposite speaker, it also accounted for diffraction caused by the listener's head. When sound from the left speaker hits the listener's head, the head itself causes the soundwave to travel around the head from the left side to the rigt side, again on a delayed basis. The Carver circuit compensates for this as someone described above (delayed, inverse phase signal sent to the right speaker).

I have (somewhere in a closet) a holography generator. It does create, with most recordings, an extremely wide soundstage, with some images sounding like they are completely to the side and quite close to the listener's head. The sound is quite phasey and not entirely realistic (though fascinating).

There are recordings that were made with these compensating signals built into the recording in order to throw images way outside the speaker. Roger Water's "Amused to Death" is an example. A less extreme (more subtle) use can be found on a Nouvelle Vague "Nouvelle Vague" recording (French girl group doing terrific covers on Brit pop/rock). If you want a rough idea of what the Carver circuit can do, get the Roger Water recording.

yes, the head causes additional time delay.
It also causes the 'downstream' side to get fewer high frequency part of the sound. That's the reason for the 6" speaker seperation on some Polk models seeking to mimic this circuit.

In nature, the time delay, spectrum difference, loudness and several other things are all 'cues' to location and direction and distance.
VITAL to survival.

The reason for the delay is that you want the out-of-phase right channel signal injected into the left channel to arrive at the left ear at the same time as the (in phase) acoustic right channel signal arrives at the left ear, resulting in cancellation of the right channel at the left ear. Similar logic applies to the out-of-phase left channel signal injected into the right channel. In other words we want the left ear to hear only the left speaker and the right ear to hear only the right speaker.

There are always side effects. Mixing the delayed out-of-phase signals cross channel results in some comb filtering, which explains the phasey sound noted by some listeners.

The effect is record-able, and the c9 had a sticker on the back warning the user that it was illegal under the Sonic Hologram license to use the device to make recordings.

That Ambiophonic device looks interesting.

"Sonic Holography was one of Bob's ploy's to get people to purchase his products. These names really meant nothing."

Well, the name is descriptive of the effect and the effect does in fact work with the right gear set up properly for it.

Its merits versus other approaches or whether one likes it or not is a different discussion.

Left + right and left - right. It does work very well with the C-1 preamp and/or the outboard C-9 unit. It cancells interaural crosstalk and the sound is really good, but you must set up the speakers correctly. It's not a ploy of any sort. If you get the McIntosh pre just add a C-9 to it.