I know it's been a bit, but I got to A/B the two, the Jim Williams mod LXP-15II and the PCM90. I have only a/b'd on some rough drum tracks, but I've tried to get the same general verb on the presets of each to get a feel for it. Well, the PCM has a lot more reverb presets since it is a dedicated reverb processor. I've mainly compared the plates and halls. The PCM sounds deeper, like the sound should be coming out of a 3 unit rack. The sound is what I would expect to hear from a 3 or 4 unit sized rack box, deep and big are the only adjectives that are coming to mind, spatially 3d. Now the LXP is no slouch by any means, and the Dark Hall setting I'm thinking will be the preset that ends in the effects sends on my board, unless I track with the Rich Plate on the PCM (love it on drums, as well as Cool Plate and Real Hall) and side chain it. Anyway, the quality of the LXP is wonderful, and I can't wait to mess with it some more. Drum Plate and Warm Plate were two I was comparing against the PCM. The tails sound great. Not quite as "deep" as the PCM in sonic depth, but a wonderful sounding box. I really need to explore both more, and will in time, but thought I'd give an honest update. If I get around to it, I'll post some clips with a couple of different presets so you can hear each.