Best small, desktop speakers, $500 or under (new or used)

Hold out for a used pair of Silverline Minuets — you wont be sorry.  And I’d cross the Clairaudient speakers off your list.  They’re awful.  I had the 1+1 on demo and were the worst speakers I’ve ever heard.  Took them to a buddy’s house to hear them in his system and he laughed at how bad they were.  Rolled-off, muddy highs, hollow- sounding mids, and no dynamics whatsoever.  IMO someone at TAS got paid for a positive review because these things are awful.  Did I mention they’re awful?  Anyway, hope this helps, and best of luck in your search. 

Clairaudients are awful...well, that might explain why they can be found for $450 or $550 online.

Would love to find Rogers, Spendor, Harbeth in this price range...a bit of a challenge! And KLH, too!

So, let me let one small confession slip... I presently have some small Pinnacle PN5+ speakers which are a good size and sound ok. I just figured these are pretty mediocre compared to what folks are saying here. And...the company is out of business, too. But maybe there’s a tweak there or I just have something better than I think I do. They were never expensive speakers but...

The Triangle Borea BR02 is $450... they are getting great reviews.  Check them out too.

I have 2 pair of Realistic (Radio Shack) Minimus 7s, they're OK. I used one set for surround rears for years on the shelf behind the couch. I seriously upgraded them to Martin Logan Motion 2s (with AMT) These will work on a desktop 110-25000 Hz. Put a $40 CyberAcoustics under the desk to fill in lower freqs. They are worth the $240/pr while they last. Call Safe and Sound and ask if they have any refurbs ($150) laying around.

The holy grail of desktop speakers are the Monsoon Planar 9s. They are like mini Magnapans. The catch is that the controller connects to the amp\sub via a 9 pin mini din and they are All broken. If you can microsolder an old Mac printer cable would work. I have the pin assignments. Otherwise you can jury rig them to another amp/sub (like I did for my TV) but the SQ will probably be inferior to OEM.
If you are ambitious, Madisound is the winner. I love the pair I built from scratch 25 years ago before they marketed cabinet kits. Probably cost prohibitive by the time you match an amp to them. 
Unless you are dead set on your own amp I recommend powered speakers for better SQ and less clutter. Review the rec's above. Even though I have not heard the Vanatoos I'll wager that they sound the best due to bi-amping (matched to the drivers.)and radiators.  Only a direct showdown could prove me wrong.
If you want to max out your $500 my vote is for Vanatoo Transparent One Encore B-Stock.  You'll probably have to make a request to reserve a pair.

Thanks so much. I'm not ambitious to build for desktop. I am open to de-cluttering. The idea of a bi-amped speaker for desktop was something I would have thought overly- fancy for that application, but there you go!