Stephen, I doubt you'll get an outboard unit at your cap price. Back in '95 & '96 the outboard demodulators were pretty much all $250 and up. Some of the hi-end brands floated 'em out for perverse prices above $500! It's realistic to find one for, say, 120-$200, IMO.
To be honest with you, you don't need the outboard demod unless you want it for more distant future use. Just watch the thang in PCM a few times and when you get the head unit with the demod, decide if the AC-3 track is worth listening to. IMO, these films sound better in PCM via the digital output. Sure, they put in a cute echo in STAR WARS when Luke is down in the canyon, where he got clubed by totally ugly aliens and saved by Obi Wan, that's about the highlight of the AC-3 track IMO.
Remember, the PCM is uncompressed, CD-quality sound. LD's are big CD's that do more, like, basically. Back to STIR WARZ, I'd say that the last one has the best AC-3 track. I really prefer PCM on the first two myself. If you wanna get an LD that really blows it out in AC-3 get, say, STAR WARZ PHANTOM DENTIST, COURAGE UNDER FIRE, or WHITE SQUALL, IMO. Best wishes from Laserland!
