Nice windfall!
A 1st world problem to be sure, but a tough one!
Some misc comments:
Different speakers
I would not change to another speaker without first having the opportunity to compare them with yours in the same room (unless you can live with the return policy).
You might peruse through this thread and see if there is something interesting close by:
http://www.avsforum.com/forum/89-speakers/1354492-i-ll-demo-my-speakers-other-enthusiasts-thread.html
Many of us would enjoy someone bringing over some quality speakers and comparing them against what we have.
If you have a BestBuy with Magnolia Room nearby, you might see if they have a pair of Martin-Logans from their motion series. I heard the model 20 and thought they sounded pretty good for something from BestBuy. I think you can do better buying Philharmonic or Salk, but it is always good to listen to good speakers and see if you notice good or bad vs your own. Of course you should check out their electrostatics while you are there!
Ultras
Sticking with your Ultras may be the best course of action. It is hard to find fault with them and they look great in your setup.
However, I would look at the towers (via free 45 day trial) with a very skeptical eye. $2000 for a pair of towers is kind of on the threshold of eliminating the resonances in the larger box. Their description includes lots of good things - FEA design, bracing, separate chambers, thick walls; but the proof is in the sound. I like to use Steely Dan for checking coloration because they are so tight in the mid-upper bass range that the coloration comes off as sloppy compared to a BS (however the coloration can sound very rich and full on something like Hotel California - so personal opinion is important as well)!
Also note that the mids are in sealed chambers. So they might not sound as much like the Ultra BSs as you expect. Give them a careful listen before deciding to move from the BS to towers.
On less expensive towers, I almost always detect some coloration in the mid-upper bass.
If you try the towers... for music, try them w/o the subwoofers. With a 28Hz low end and a little room gain, you won't need subs for (typical) music.
Salk vs Philharmonic
Definitely the right place to be looking! If you identify a couple of considerations, contact Dennis Murphy to discuss. He is, of course, familiar with both and will give you straight answers on either. My opinion is you cannot find better value than Philharmonic. Value is what Dennis is about! However, if you start looking at custom furniture grade finishes on your Philharmonic speakers, the Salk speakers get much more competitive. If you have read many of Murphy's posts, I think you realize that he will not put his own sales ahead of Salks, nor will he put Salk's sales ahead of his own. I believe he will put your objectives as best you explain them ahead of either. I think he is pretty idealistic about really just wanting to help people find their best "happy-audio-place"!
Amp
Tough call on the Monolith! IIRC, the extra channels cost about $100 a piece after the first 2 or 3. Knowing I'm in for life, I think I'd have to get the 7 channel (at least 5). Remember, if you get extra channels but only use 3, just use the two end and central channel modules in the amp so the heat is spread out. (you might also want to run some outdoor speakers out to the deck or add a pair in an adjacent room).
The Monolith is hard to pass up with it's ATI heritage and top notch performance, it is definitely a value leader! It is an amp that you would probably never consider upgrading from
Stepping down the cost, the best value is the $600 Outlaw 5000.
If you scroll down to the chart just above the "Ground Analysis and FFT..." you'll see it produces 170 WRMS into 2 channels at 8 ohms and 240 into 4 Ohms and 135WRMS with all 5 channels driven!
http://www.audioholics.com/amplifier-reviews/outlaw-5000/measurements
My point is that even though it is a 5 channel amp, for $600, it competes well with any $600 two channel amp and gives you the flexibility of 3 additional channels. If you end up looking at the Monolith as pricing you out of the speakers you want, you might consider the Outlaw as a more cost effective way to off-load the Marantz.
The most cost effective solution (depending on how hard you drive it) is probably to put the "Eco" mode of your Marantz on "Auto". Between that and the cooler, I think you will have a very cool (and long) running AVR!
That is the long of it, but $3000 will buy you a pair of Philharmonic BMR and a "less endowed" version of the Monolith. I would try hard to make the effort to listen to the BMR's. Dennis may know a buyer in your area who will let you listen to them and bring your Ultras to compare.