Best option for Amp upgrade...

Pass X250.8,  Parasound JC1,  modded McCormack - all great amps, just a matter of personal preference...a friend has a SMC modded DNA 225 that is awesome...

Since you have a CJ preamp,why not get a CJ amp?
http://conradjohnson.com/mf2550-and-mf2275-solid-state-amplifiers/

Wow!  If you have the money for the full SMc Audio modification to your present amp, GO FOR IT!  I have an SMc modded DNA-1.  The Revision A+ mod was done about a decade or so ago.  It sounds fantastic and I'm sure if I had it upgraded to the Signature mod offered now it would be even better.  Steve McCormack is a great guy to talk to and work with and is every bit the designer as John Curl is at Parasound.

In talking with Steve he expressed strongly held opinions on the parts that he selects for his mods down to the quality of the fuses he uses.

I'm sure there are many fine amps you could buy with your generous budget.  If you're in the mood for a new shiny beast that's cool, but if you let Steve do the full monty on your DNA 500 you will be a very satisfied listener.  The DNA concept design of mating each output transistor with its own generous capacitor does, as Steve intended, yield a "quick" sound with clean impactful initial note impacts.  PRAT!

All the best!

shoff,

I suggest you sell your McCormack DNA-500, especially if you think you can get $3k for it. It’s likely got a few years on it and certain internal components don’t last indefinitely, especially power supply capacitors.

Your Rockport Mira II speakers are very good spkrs that are not very efficient that usually sound their best with a powerful amp or amps driving them.
I think a pair of D-Sonic M3-1500-M class D monoblocks would be a very good match for your speakers and CJ preamp. Plenty of clean, undistorted power to drive your somewhat inefficient speakers with enough in reserve for increased dynamic range. Here’s a 6Moons review:

www.6moons.com/audioreviews/dsonic/1.html

Because these amps are so neutral in nature and add little sound of their own, the sound characteristics of your tubed CJ preamp will be the main factor in the flavor of your system’s sound. Good news if you like the sound of your preamp.
These amps are based on newer Pascal class D power modules that combine the power module with a switch mode power supply (smps) on a single board. You’ll notice the review lists the amps as D-Sonic M2-1500-M models. D-Sonic’s owner, Dennis Deacon, decided to change the model name to M3-1500-M right after this review to signify the change in the internal power modules being used and their increase in performance.
There’s little risk in buying tese and trying them in your system since D-Sonic offers a 30-day in-home trial period with a "no questions asked" return policy. I doubt he has many refund requests.

Tim

The DNA500 is already a pretty hi-rez and detailed amp even in stock form.  I think what you may be hearing, despite its many other considerable strengths, are some limitations of your preamp -- at least that's what reading reviews of your pre lead me to believe.  Have you considered tube rolling?  I'm not familiar with your interconnects, but that's another area maybe worth exploring to tweak the sound of your system a bit.  Just throwing some other thoughts out there FWIW.  Best of luck.