Aragon 4004mkII OR Adcom GFA 555 II

Ive owned both. the aragon wont be in your face as much as the adcom. Much more refined sound, its a great amp comparring to more expensive amps, Be careful its very detailed so if you have hot highs already it might put things over the top.

This is a lateral move.

Try A Odyssey Stratos.

The Aragon is definately the better of the two; actually as bigger powetred amps go ... a great amp at used prices. More resolution, finesse, and .... more transparent for the buck.

The Aragon will be smoother but too laid back and quite boring in my opinion. Chose a McCormack DNA 1 when I auditoned both of these years ago. For your Thiels, I would look for used Classe at the price range you mentioned. I just found the Aragons too slow and univolving.