I had the LNS as well, and loved them. They were getting a bit old but still worked ok.
I sold them and got the 007s MK2s which struggled with power on my 323, so I bought the 717
second hand. That worked fine, and it was a big jump from the LNS particularly the Bass.
Then I bought the 009s and now use a KGSShv. However, the 009s do sound really good on the
717, better than the 007s due to being easier to drive.
Recently I borrowed a pair of 507s, and they also sound very good, closer to the LNS is sound
but the bass is still much stronger and they are more dynamic.
So, going back to your question, the current crop of 407/507 will beat the LNS IMO,
the 007 and 009 blow them away. If you like the Stax sound you can't really go wrong.
It is how much you want to spend really.
The next jump is to use a better amp than the Stax amps IMO. But the money gets a bit silly
unless you go DIY route.
Good luck and hope this helps you.