I'd like to compare 2 sound cards and searching for a program/driver/player plug-in that enables simultaneous output to 2 (or more) sound devices.

If you are trying to do blind AB testing, you may have a more difficulty with the soundcard to amplifier/transducer part.

Feeding the soundcards can be done with two copies of the audio file running through two different software players, each specifying a different output device. There are restrictions if desiring to use ASIO drivers. I think the OS can't have two different ones active at the same time and two different soundcards will not use the same driver.

All in all you would probably be better off convincing yourself you are happy with RightMark Audio Analyzer http://audio.rightmark.org/index_new.shtml

With a multi-track editor, and two copies of the file loaded as separate tracks, and (I believe) non-ASIO drivers, it should be possible to assign the different tracks to different output devices. Not that I've ever had occasion to try, but I don't think there is any inherent limitation.

I completely forgot Audition has multi-track mode It worked perfectly in ASIO for nV SoundStorm and Audiotrak Prodigy 7.1 LT. I hope it'll work tomorrow also for Revo5.1.