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

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.

The only downside I heard with the Carver sonic holography when I used it was a noticeable loss of dynamics, mostly in the low end. It did however work as advertised if set up properly as instructed and listening smack in the sweet spot. Away from the sweet spot, the effect was detrimental.

No snake oil there. It worked exactly as advertised.

ALso I found that it worked best with more directional conventional box speakers (with a smaller sweet spot) that had coherent integration of drivers to start with, most monitors and some floorstanders. It worked with Maggie planars also but proper setup was hard.

I found it did not add anything with my OHM Walsh speakers which are essentially omnidirectional. Apparently, Carver sonic holography works best with more directional speaker designs and the effect is less noticeable with wider dispersion or omni designs.