Which Amp.

Well, since you want to get rid of your Levinson No. 23.5, I will gladly take it off your hands.

Seriously, if you want to stick to solid state, and if you like the Levinson sound, I really doubt you need to upgrade, unless you need the additional power. I upgraded from the 27 to the 23 because I really liked the sound, (and I needed the extra power) and from what I hear, the 23.5 is about a good a solid state amp as can be found.
The Levinson 33 (or33H) might be a good upgrade, as it is a mono block design, and would have more current to drive your speakers.

Now if you were getting rid of it to go to tubes, that I could understand. That would make sense, as it has a different type of sound.

I was serious, BTW, Let me know if you do decide to let go of the 23.5.

Yeah, thats a really good amp. Getting an amp thats current doesnt equate to better sound. And I sure wouldnt recommend you the the 4 series line from ML since they are basically retooled HPA Proceed amps with the ML badge on em for twice the money they once were.

If your gonna upgrade ML, grab a 3 series(334,335,336 or 33H)amp. A subtle upgrade.

Rowland monoblocks would be a good choice as well.