Best interconnects used for around $500 +?

I currently have the Audience au24se interconnects and they are very good.  I've demoed others under 1000 and these were my favorites.  They are very fast, dynamic and neutral.  I have tubes in my system and they were my personal favorites at the 1000 point.  I did demo the Wywires silvers and slightly preferred the audience au24se in my system although in another system the Wywires might be better.  For around 500 the SE's are a great value. 

From my experience, I would highly recommend you try out either used Tara labs air 1's, or Zu audio mission (new) or even better Zu audio event (if you can find used) which should all be within your budget and provide an amazing value for money. I have yet to hear IC in that price range that even come close to these. But, there are so many different cables out there that I never heard... :-)

Mrotino describes the Au24se well. I use them myself pretty much throughout my system. The only thing I'd add is that you could consider also trying Audience's Ohno ICs, which come surprisingly close to the Au24 but at a fraction of the price. 

Purist Audio Design Musaeus :-)

Forget about the AU24SE.  Should be considered the Audience SX series for ultimate musical sound just for a little more money but well worth it!  I had them both in my system and the AU24SE is not even close! 

The Audience SX delivers performance that other cable manufacturers charge 3-4X the price.