That's a good question and not one I can answer. I "think" it depends on how it was originally shot and the processing of the source material. One thing is for sure; you can't get IMAX quality projection using a lesser recording. I "think" that the difference between a converted IMAX (film) print and something shown by the Cinemark XD theaters isn't going to be dramatic. The TCL Chinese theater "IMAX" in Hollywood uses the Barco projection system (not IMAX film projector) and, therefore, can't be better (from a resolution perspective) than the Cinemark XD theaters because the Cinemark I frequent uses Barco also (though I can't say for sure that the models are the same). The IMAX theater in Irvine, on the other hand, uses an IMAX film projection system and "might" be a little bit better. This is for the video part only.
As far as audio goes, it'll depend on what kind of sound system is utilized by the theater and how they recorded and process the audio.
Bottom line is that I'm going to check it out at the IMAX in Irvine (true IMAX) and then go to the XD theater for a second viewing......all in the name of science you understand.....
t:
DJ posted some "really" cool new IMAX technology using projection on a "Technology" thread he started which looks like it could be awesome. That is a very cool thread if you're an engineering type. To put it in very simple terms, I look at film being "analog" and projection being "digital". Both have their strengths and weaknesses, but as digital get higher and higher with regard to resolution, those strengths start to favor the digital side.