Best used amp in the $1500 range

Nothing brings home weight and dynamics like a big class A amp. I've heard really powerful AB designs do it as well, but only at really high volume. Krell and Levinson come to mind, but not usually at that price point. You might find an older krell KSA-100 or similar Levinson since you are looking used, but be careful as class A amps might need to be recapped after as little as 10-15 years.

I've never heard a Plinius amp so I can't comment, but I've found that in general, class A amps are able to convey the smallest details of a recording clearly and audibly without making your ears bleed when things get loud, and everyhing has such weight behind it. Each sound has a degree of physicality that makes the experience much more 3d and emmersive. They really work well for home theater and music. The downside of course is size, expense, heat... so they aren't for everyone.