Difference between NAD 2400PE & 2400 THX

I have been upgrading my system lately and selling off some old gear. The following question has been asked repeatedly of me.
NAD produced the 2400 amplifier and the 2400THX amplifier. There were models that carried the THX logo and others that did not. Does anyone know if there are any differences in these two amplifiers sonically, transformers, anything at all? It appears that the 2400 versions were made before and after the THX version. NAD archives only list the 2400 not seperate versions. I used them in the bidged mode which according to hookup instructions when bridged you don't use the THX inputs anyway. Any help appreciated.
I can't say with absolute certainty that the two amps are identical, but I can tell you that the "THX" appelation is largely meaningless. The right to use the "THX" trademark and logo on a piece of audio equipment is subject to two factors (neither of which has much to do with insuring "better" audio quality):

1. "THX" publishes a set of performance standards that THX-licensed equipment must meet. These standards were devised originally with movie theaters in mind. With HT equipment, the standards pertain primarily to sustained and peak power output, and distortion levels, plus adherence to some other performance criteria that the "THX" folks think are relevant to good HT sound. In point of fact, almost all better quality audiophile amps meet or exceed these standards. Many people assume that the "THX" trademark and logo is a guarantee of better performance, which "ain't necessarily so". In short, for better quality amps, the "THX" logo is mainly a marketing gimmick.

2. The REAL meaning of the "THX" trademark and logo is that the manufacturer has paid a licensing fee to use the logo, which is assumed to be a strong selling feature to HT enthusiasts.

As far as I know, there are no significant differences between the two NAD 2400 amps, except in how the power output is rated. For practical purposes, it's a non-issue.
I'm not sure about the THX, but the PE stood for "power envelope." The NAD's in this series had 6db headroom, or in other terms, pretty high current for a given watts into 8 Ohms rating.