Using a Pre-Out to Bi-amp

Amp 1 is 'quicker' or 'slower' to transfer a signal than #2.
Say....about 1/2 milisecond. 1/2 milisecond at the speed of SOUND translates into about 6 or 7 inches.
If the 'late' signal gets to the tweeter, than it will appear as out of phase/ time smeared info. A 3-way system would make matters worse.
Right, of course, about transducer in amp to convert electrical to sound, but IF there is some reason for the signal to take longer to go THRU the amp, there you are.
This, in all fairness, is theoretical. BUT, it is easily tested with a signal generator and dual trace o-scope. If you were only dealing with a length of wire, it'd have to be nearly 1800 miles long to produce such a delay. But, toss in some caps / inductors / RC / LC networks and it could happen.
It is not the distance a signal travels, but the time it takes.
If I were prone to Bi-Amp, I'd use identical amps.
Since this is testable, I have no worries that someone hasn't already thought of this, measured it and discarded the idea.
Another good reason to use identical amps is possible phase invert of one but NOT both. This'll throw most people and cause no end to image / focus problems until properly diagnosed.

Test w/O-Scope is confirmation.
Your reasoning is overall sound, but some amps may contain circuitry which acts in a time delay manner and May be audible. Something over 1/4 millisecond should do it.
I was just suggesting time delay as a possible occurance. I doubt it is really an issue, but lesser things have been turned into issues.
One thing NoBody mentioned was to have amps which are a match in Timbre. Put Rotel and NAD together and You've got a catfight. Or how 'bout Krell and Mac?

The other issue I missed was that many receivers will have different circuitry going into internal amps vs the pre out. I highly doubt that the internal amp signal passes by the pre-outs before being utilized. This should further muddy the waters. A few milliseconds difference is all it takes to kill that "magic" we are all looking for.