Upgrade path

Keep in mind the value of your current Dunlavys.
Others might disagree with your power observations with Dunlavys, but you might(!) be on to something. I had a friend go from two 200 watt mono amps to four identical factory matched of the same amps, and the improvement was much greater than either of us expected with his SC IV's. I'm still not sure whether it was the extra power, the longer Class A bias, or some combination there in. 
The SC IVa' are capable of more of the things you are seeking than you might think. Unfortinately they don't show up on the used market too often. The SC V's show up more often and usually for less than $6k, so with the sale of your IV's you should be within budget. One caveat: a lot of V's and VI's were used in recording studios and might have seen a lot of (ab)use.

I would most likely replace the power amp first. You never know how your speakers can sound until you give them the right amp.

I wonder how a Sanders Magtech amp would sound with the Dunlavys?

I was kinda thinking the same. I have a line on a older Mac 2500 which has been rebuilt by Mcintosh and comes with a one year warranty. I know many don't care for Mac amps but it's in my price range and has a warranty. Grew up in a house with Mac gear all my younger years and will I have herd other big names do this or that better Mac has always been that middle of the road amp that I could listen to for hours at a time.. Will have to look up Sanders amps as I'm not familiar with them.