Best Pre-amp for $500??

Not sure what the rest of your system is so I'll throw a dart with my bad eye on this one. Guessing your system is totally digital as you expressed no need for a phono stage. Finding something for $5-700 is tuff so here's what I'd do; find a used Cambridge 851C. It has a great preamp, killer DAC and sounds great going directly into an amp and it has a nice remote. I've listened to the entry Parasound Halo preamp and it doesn't get close to the preamp or DAC of the 851C. If you're amp has balanced inputs the 851C has balanced out too. As a CDP it is as good as you're going to get without selling the farm and if you're using you're computer or media server it's built for that too; all kinds of digital inputs. You're going to have to increase your budget a little but you'll be happy. It's built very well too if that matters.

Cambridge 851D might be something to look at if you don't spin CDs or have another player you want to keep. I've not heard the 851D, but would think its for the most part an 851C without the transport.

A sunfire amp drives Maggies.  Outboard DAC is dealing with an Apple TV and Mac/iTunes.  Still have a Cal Audio CD player, and sometimes use a Yamaha tuner.

I had a Sonic Frontiers pre-amp but it blew one channel and the remote is busted too.  

Get the aragon 28k preamp if u can find one.
I have owned it for 20yrs.
In those years, it beats all my new purchases to replace it. Musical fidelity ac3r, rogue audio, simaudio 740p.

During my process to upgrade it, i brought it for comparison with accuphase 2410, ayre kx5, ayre k5xemp, jeff rowland capri, mbl preamp, the aragon never paled in comparisonin terms of Clarity, openess and dynamics.

I finally bought the sim 740p based on reviews and without audition.

Sold the 740p after 3months. 

Still stuck with this vintage, its simply irreplaceable.

Oh yes, forgot to mention it also sounded way clearer than the mark levinson 326s