The PCM 91 has been around for quite a long time, not as long as the PCM70 etc. and it is an excellent effects unit. It is a high quality multi effects unit, on a par with the 480L but without the remote control. This unit is in good working condition however 2 of the knobs are missing their knob caps and there is a little rack rash.
These days it is available at a very attractive price, £750
LEXICON SAY :
The PCM 91 offers Lexicon’s highest quality reverbs in a compact, affordable package with a powerful interface which allows both easy access and a wealth of programming capabilities for the sound designer. All of the features of the acclaimed PCM 90 are included, plus full AES/EBU I/O, Dual Reverb algorithms, and presets with dynamic spatialization effects for 2-channel or surround applications
Listen to some of the Lexicon PCM91 audio effects on this You Tube video
E&oe.